Compositions and methods and uses relating thereto

ABSTRACT

A quaternary ammonium compound of formula (I): 
                         
wherein R 0 , R 1 , R 2  and R 3  is each independently an optionally substituted hydrocarbyl group, X is a linking group, R 4  is an optionally substituted alkylene group, R 5  is hydrogen or an optionally substituted alkyl, alkenyl or aryl group, and n is 0 or a positive integer, provided that n is not 0 when R 5  is hydrogen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application under 35 U.S.C.371 of International Application No. PCT/GB2018/050840, filed on Mar.28, 2018, and entitled COMPOSITIONS AND METHODS AND USES RELATINGTHERETO, which in turn claims priority to and benefit of Great BritainPatent Application No. 1705091.5, filed Mar. 30, 2017, which isincorporated by reference herein in its entirety for all purposes.

FIELD

The present invention relates to novel quaternary ammonium compounds, tocompositions comprising these compounds and methods and uses relatingthereto. In particular the invention relates to compositions, methodsand uses for improving the performance of engines, especially dieselengines, using fuel additives. In particular the invention relates toadditives for diesel fuel compositions for use in diesel engines withhigh pressure fuel systems.

BACKGROUND

Due to consumer demand and legislation, diesel engines have in recentyears become much more energy efficient, show improved performance andhave reduced emissions.

These improvements in performance and emissions have been brought aboutby improvements in the combustion process. To achieve the fuelatomisation necessary for this improved combustion, fuel injectionequipment has been developed which uses higher injection pressures andreduced fuel injector nozzle hole diameters. The fuel pressure at theinjection nozzle is now commonly in excess of 1500 bar (1.5×10⁸ Pa). Toachieve these pressures the work that must be done on the fuel alsoincreases the temperature of the fuel. These high pressures andtemperatures can cause degradation of the fuel. Furthermore, the timing,quantity and control of fuel injection has become increasingly precise.This precise fuel metering must be maintained to achieve optimalperformance.

Diesel engines having high pressure fuel systems can include but are notlimited to heavy duty diesel engines and smaller passenger car typediesel engines. Heavy duty diesel engines can include very powerfulengines such as the MTU series 4000 diesel having 20 cylinder variantsdesigned primarily for ships and power generation with power output upto 4300 kW or engines such as the Renault dXi 7 having 6 cylinders and apower output around 240 kW. A typical passenger car diesel engine is thePeugeot DW10 having 4 cylinders and power output of 100 kW or lessdepending on the variant.

A common problem with diesel engines is fouling of the injector,particularly the injector body, and the injector nozzle. Fouling mayalso occur in the fuel filter. Injector nozzle fouling occurs when thenozzle becomes blocked with deposits from the diesel fuel. Fouling offuel filters may be related to the recirculation of fuel back to thefuel tank. Deposits increase with degradation of the fuel. Deposits maytake the form of carbonaceous coke-like residues, lacquers or sticky orgum-like residues. Diesel fuels become more and more unstable the morethey are heated, particularly if heated under pressure. Thus dieselengines having high pressure fuel systems may cause increased fueldegradation. In recent years the need to reduce emissions has led to thecontinual redesign of injection systems to help meet lower targets. Thishas led to increasingly complex injectors and lower tolerance todeposits.

The problem of injector fouling may occur when using any type of dieselfuels. However, some fuels may be particularly prone to cause fouling orfouling may occur more quickly when these fuels are used. For example,fuels containing biodiesel and those containing metallic species maylead to increased deposits.

When injectors become blocked or partially blocked, the delivery of fuelis less efficient and there is poor mixing of the fuel with the air.Over time this leads to a loss in power of the engine and increasedexhaust emissions and poor fuel economy.

Deposits are known to occur in the spray channels of the injector,leading to reduced flow and power loss. As the size of the injectornozzle hole is reduced, the relative impact of deposit build up becomesmore significant. Deposits are also known to occur at the injector tip.Here they affect the fuel spray pattern and cause less effectivecombustion and associated higher emissions and increased fuelconsumption.

In addition to these “external” injector deposits in the nozzle hole andat the injector tip which lead to reduced flow and power loss, depositsmay occur within the injector body causing further problems. Thesedeposits may be referred to as internal diesel injector deposits (orIDIDs). IDIDs occur further up inside the injector on the criticalmoving parts. They can hinder the movement of these parts affecting thetiming and quantity of fuel injection. Since modern diesel enginesoperate under very precise conditions these deposits can have asignificant impact on performance.

IDIDs cause a number of problems, including power loss and reduced fueleconomy due to less than optimal fuel metering and combustion. Initiallythe engine may experience cold start problems and/or rough enginerunning. These deposits can lead to more serious injector sticking. Thisoccurs when the deposits stop parts of the injector from moving and thusthe injector stops working. When several or all of the injectors stickthe engine may fail completely.

IDIDs are recognised as a serious problem by those working in the fieldand a new engine test has been developed by the industry basedorganisation, the Coordinating European Council (CEC). The IDID DW10Ctest was developed to be able to discriminate between a fuel thatproduces no measurable deposits and one which produces deposits thatcause startability issues considered unacceptable. The objective of thetest is to discriminate between fuels that differ in their ability toproduce IDIDs in direct injection common rail diesel engines.

The present inventors have studied internal diesel injector deposits andhave found that they contain a number of components. As well ascarbonaceous deposits the presence of lacquers and/or carboxylateresidues can lead to injector sticking.

Lacquers are varnish-like deposits which are insoluble in fuel andcommon organic solvents. Some occurrences of lacquers have been found byanalysis to contain amide functionality and it has been suggested thatthey form due to the presence of low molecular weight amide containingspecies in the fuel.

Carboxylate residues may be present from a number of sources. Bycarboxylate residues we mean to refer to salts of carboxylic acids.These may be short chain carboxylic acids but more commonly long chainfatty acid residues are present. The carboxylic residues may be presentas ammonium and/or metal salts. Both carboxylic acids and metals may bepresent in diesel fuel from a number of sources. Carboxylic acids mayoccur due to oxidation of the fuel, may form during the combustionprocess and are commonly added into fuel as lubricity additives and/orcorrosion inhibitors. Residual fatty acids may be present in the fattyacid methyl esters included as biodiesel and they may also be present asbyproducts in other additives. Derivatives of fatty acids may also bepresent and these may react or decompose to form carboxylic acids.

Various metals may be present in fuel compositions. This may be due tocontamination of the fuel during manufacture, storage, transport or useor due to contamination of fuel additives. Metal species may also beadded to fuels deliberately. For example, transition metals aresometimes added as fuel borne catalysts to improve the performance ofdiesel particulate filters.

The present inventors believe that one of the many causes of injectorsticking occurs when metal or ammonium species react with carboxylicacid species in the fuel. One example of injector sticking has arisendue to sodium contamination of the fuel. Sodium contamination may occurfor a number of reasons. For example, sodium hydroxide may be used in awashing step in the hydrodesulfurisation process and could lead tocontamination. Sodium may also be present due to the use ofsodium-containing corrosion inhibitors in pipelines. Another example canarise from the presence of calcium from, for example, interaction withor contamination with a lubricant or from calcium chloride used in saltdrying processes in refineries. Other metal contamination may occur forexample during transportation due to water bottoms.

Metal contamination of diesel fuel and the resultant formation ofcarboxylate salts is believed to be a significant cause of injectorsticking. The formation of lacquers is yet another major cause ofinjector sticking.

One approach to combatting IDIDs and injector sticking resulting fromcarboxylate salts is to try to eliminate the source of metalcontamination and/or carboxylic acids or to try to ensure thatparticularly problematic carboxylic acids are eliminated. This has notbeen entirely successful and there is a need for additives to providecontrol of IDIDs.

Deposit control additives are often included in fuel to combat depositsin the injector nozzle or at the injector tip. These may be referred toherein as “external injector deposits”. Additives are also used tocontrol deposits on vehicle fuel filters. However additives which havebeen found to be useful to control “external deposits” and fuel filterdeposits are not always effective at controlling IDIDs. A challenge forthe additive formulator is to provide more effective detergents.

SUMMARY

It is an aim of the present invention to provide methods and uses whichimprove the performance of a diesel engine, especially a diesel enginehaving a high pressure fuel system. This may be achieved for example bypreventing or reducing the formation of IDIDs and/or by reducing orremoving existing IDIDs. The invention provides methods and uses whichcontrol “external injector deposits” and/or fuel filter deposits.

Reducing or preventing the formation of deposits may be regarded asproviding “keep clean” performance. Reducing or removing existingdeposits may be regarded as providing “clean up” performance. It is anaim of the present invention to provide “keep clean” and/or “clean up”performance.

Many different types of compounds are known in the art for use asdetergent additives in fuel oil compositions, for the control ofdeposits in engines.

The present invention relates to novel quaternary ammonium compoundshaving an ester counterion that is the partial ester of a polycarboxylicacid that are useful as detergents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of a test procedure consisting of main run cyclesfollowed by soak periods; and

FIG. 2 is a graph of all exhaust temperatures with <30° C. deviation.

DETAILED DESCRIPTION

According to a first aspect of the present invention there is provided aquaternary ammonium compound of formula (I):

wherein R⁰, R¹, R² and R³ is each independently an optionallysubstituted hydrocarbyl group, X is a linking group, R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is 0 or a positive integer, providedthat n is not 0 when R⁵ is hydrogen.

Preferably each of R⁰, R¹, R² and R³ is an optionally substituted alkyl,alkenyl or aryl group.

As used herein, the term “hydrocarbyl” substituent or group is used inits ordinary sense, which is well-known to those skilled in the art.Specifically, it refers to a group having a carbon atom directlyattached to the remainder of the molecule and having predominantlyhydrocarbon character. Examples of hydrocarbyl groups include:

(i) hydrocarbon groups, that is, aliphatic (which may be saturated orunsaturated, linear or branched, e.g., alkyl or alkenyl), alicyclic(e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic (includingaliphatic- and alicyclic-substituted aromatic) substituents, as well ascyclic substituents wherein the ring is completed through anotherportion of the molecule (e.g., two substituents together form a ring);

(ii) substituted hydrocarbon groups, that is, substituents containingnon-hydrocarbon groups (e.g., halo (especially chloro and fluoro),hydroxy, alkoxy, keto, acyl, cyano, mercapto, alkylmercapto, amino,alkylamino, nitro, nitroso, and sulphoxy);

(iii) hetero substituents, that is, substituents which, while having apredominantly hydrocarbon character, in the context of this invention,contain other than carbon in a ring or chain otherwise composed ofcarbon atoms. Heteroatoms include sulphur, oxygen, nitrogen, andencompass substituents as pyridyl, furyl, thienyl and imidazolyl. Ingeneral, no more than two, preferably no more than one, non-hydrocarbonsubstituent will be present for every ten carbon atoms in thehydrocarbyl group; typically, there will be no non-hydrocarbonsubstituents in the hydrocarbyl group.

In this specification, unless otherwise stated references to optionallysubstituted alkyl groups may include aryl-substituted alkyl groups andreferences to optionally-substituted aryl groups may includealkyl-substituted or alkenyl-substituted aryl groups.

The quaternary ammonium salt of the present invention may be prepared byany suitable means. Suitable methods will be known to the person skilledin the art.

In some embodiments, R⁰ may be a lower alkyl group and the quaternaryammonium compound is prepared from an ester of formulaR⁰OOCXCOO(R⁴O)_(n)R⁵. In such embodiments R⁰ is preferably methyl.

In some embodiments the quaternary ammonium salt may be prepared from anester quaternising agent of formula RCOOR⁰ followed by an ion exchangereaction with an acid of formula HOOCXCOO(R⁴O)_(n)R⁵. In suchembodiments R may be an optionally substituted aryl or alkyl group or anester. For example R⁰ may be methyl and RCOOR⁰ may be methyl salicylateor dimethyl oxalate.

In some embodiments R⁰ is a C1 to C5 alkyl group, preferably methyl.

In preferred embodiments the quaternary ammonium compound is preparedfrom a tertiary amine, an acid-activated alkylating agent and an acid.Thus R⁰ is preferably the residue of an alkylating agent.

In preferred embodiments the first aspect of the present inventionprovides a quaternary ammonium compound which is the reaction productof:

(a) a tertiary amine of formula R¹R²R³N;

(b) an acid-activated alkylating agent; and

(c) a compound of formula HOOCXCOO(R⁴O)_(n)—R⁵ wherein R⁴ is anoptionally substituted alkylene group, R⁵ is hydrogen or an optionallysubstituted alkyl, alkenyl or aryl group and n is 0 or a positiveinteger, provided that n is not 0 when R⁵ is hydrogen.

According to a second aspect of the present invention there is provideda method of preparing a quaternary ammonium salt, the method comprisingreacting (a) a tertiary amine of formula R¹R²R³N with (b) anacid-derived alkylating agent in the presence of (c) a compound offormula HOOCXCOO—(R⁴O)_(n)—R⁵, wherein R⁴ is an optionally substitutedalkylene group, R⁵ is hydrogen or an optionally substituted alkyl,alkenyl or aryl group, and n is 0 or a positive integer, provided that nis not 0 when R⁵ is hydrogen.

Preferred features of the first and second aspects of the invention willnow be described.

In this specification any feature of any aspect of the invention may becombined with any feature of any other aspect as appropriate.

X is a linking group. Preferably X is an optionally substituted alkyleneor arylene group. X is further defined herein.

The present invention relates to a composition, a method and a useinvolving a quaternary ammonium salt. This compound may be referred toherein as “the quaternary ammonium salt” or as “the quaternary ammoniumcompound”.

The quaternary ammonium salt may comprise a single compound. In someembodiments mixtures containing more than one quaternary ammonium saltadditive may be used. References herein to “a quaternary ammonium salt”of the invention or “the quaternary ammonium salt” include mixturescomprising two or more such compounds.

Component (a) used to prepare the quaternary ammonium salts of thepresent invention is a tertiary amine. Any suitable tertiary amine maybe used.

In some embodiments of the present invention the tertiary amine may be asmall compound of low complexity and low molecular weight. In someembodiments the tertiary amine may be a complex molecule and/or amolecule of high molecular weight which includes a tertiary aminemoiety.

The tertiary amine compounds of the present invention preferably do notinclude any primary or secondary amine groups. In some embodiments theymay be derived from compounds including these groups but preferablythese have been subsequently reacted to form additional tertiary aminespecies. The tertiary amine compound used as component (a) may containmore than one tertiary amine group. However tertiary amine compoundsincluding primary or secondary amine groups are within the scope of theinvention provided these groups do not prevent quaternisation of thetertiary amine species.

Tertiary amines for use herein are preferably compounds of formulaR¹R²R³N, wherein each of

R¹, R² and R³ is independently an optionally substituted alkyl, alkenylor aryl group.

R¹, R² and R³ may be the same or different. In some preferredembodiments R¹ and R² are the same and R³ is different.

Preferably each of R¹ and R² is independently an optionally substitutedalkyl, alkenyl or aryl group having from 1 to 50 carbon atoms,preferably from 1 to 40 carbon atoms, more preferably from 1 to 30carbon atoms.

Each of R¹ and R² may be optionally substituted with one or more groupsselected from halo (especially chloro and fluoro), hydroxy, alkoxy,keto, acyl, cyano, mercapto, alkylmercapto, dialkylamino, nitro,nitroso, and sulphoxy. The alkyl groups of these substituents may befurther substituted.

Preferably each of R¹ and R² is independently an optionally substitutedalkyl or alkenyl group. Preferably each of R¹ and R² is independently anoptionally substituted alkyl group. Preferably each of R¹ and R² isindependently an optionally substituted alkyl or alkenyl group havingfrom 1 to 50 carbon atoms, preferably from 1 to 40 carbon atoms, morepreferably from 1 to 30 carbon atoms, suitably from 1 to 20 carbonatoms, preferably from 1 to 12 carbon atoms, more preferably from 1 to10 carbon atoms, suitably from 1 to 8 carbon atoms, for example from 1to 6 carbon atoms.

In some embodiments each of R¹ and R² is methyl and R³ is a C₆ to C₃₆,preferably a C₁₀ to C₃₀, alkyl or alkenyl group.

In some embodiments R¹ is methyl and each of R² and R³ is a C₆ and C₃₈,preferably a C₁₀ to C₃₀ alkyl or alkenyl group.

Preferably R¹ is an optionally substituted alkyl or alkenyl group,preferably having from 1 to 10, preferably from 1 to 4 carbon atoms.Preferably R¹ is an alkyl group. It may be a substituted alkyl group,for example a hydroxy substituted alkyl group. Preferably R¹ is anunsubstituted alkyl group. The alkyl chain may be straight-chained orbranched. In some preferred embodiments R¹ is selected from methyl,ethyl, propyl and butyl, including isomers thereof. In some especiallypreferred embodiments R¹ is methyl or ethyl.

Preferably R² is an optionally substituted alkyl or alkenyl group,preferably having from 1 to 10, preferably from 1 to 4 carbon atoms.Preferably R² is an alkyl group. It may be a substituted alkyl group,for example a hydroxy substituted alkyl group. Preferably R² is anunsubstituted alkyl group. The alkyl chain may be straight-chained orbranched. In some preferred embodiments R² is selected from methyl,ethyl, propyl and butyl, including isomers thereof. In some especiallypreferred embodiments R² is methyl or ethyl.

In some embodiments R³ is an optionally substituted alkyl or alkenylgroup having from 1 to 50 carbon atoms, preferably from 1 to 40 carbonatoms, more preferably from 1 to 30 carbon atoms, suitably from 1 to 20carbon atoms, preferably from 1 to 12 carbon atoms, more preferably from1 to 10 carbon atoms, suitably from 1 to 8 carbon atoms, for examplefrom 1 to 6 carbon atoms.

Suitable substituents include halo (especially chloro and fluoro),hydroxy, alkoxy, keto, acyl, cyano, mercapto, alkylmercapto, amino,alkylamino, nitro, nitroso, sulphoxy, amido, alkyamido, imido andalkylimido. The alkyl groups of these substituents may be furthersubstituted.

In some embodiments R³ is an optionally substituted alkyl or alkenylgroup, preferably having from 1 to 10, preferably from 1 to 4 carbonatoms. Suitably R³ is an optionally substituted alkyl group. In someembodiments R³ is an unsubstituted alkyl group, for example a C₁ to C₁₀,suitably a C₁ to C₆ or a C₁ to C₄ alkyl group. The alkyl group may bestraight chain or branched.

In some preferred embodiments R³ is a substituted alkyl group. Preferredsubstituents include alkoxy and hydroxy groups.

In some embodiments the alkyl chain may be interrupted by one or moreheteroatoms, for example one or more oxygen atoms.

In some preferred embodiments R³ is a hydroxy-substituted alkyl group.The alkyl chain may be straight-chained or branched. In some especiallypreferred embodiments R³ is a hydroxyethyl group.

In one embodiment R³ is a hydroxyethyloxyethyl group.

In some embodiments each of R¹, R² and R³ is independently selected froman alkyl or hydroxyalkyl group having 1 to 12, preferably 1 to 6, morepreferably 1 to 4 carbon atoms.

In some embodiments trialkylamines and hydroxyalkyl diakyl amines areespecially preferred.

In some embodiments R³ is an optionally substituted hydrocarbyl group,for example an optionally substituted hydrocarbyl group having from 1 to300 carbon atoms, for example from 1 to 200 carbon atoms. R³ may be anoptionally substituted hydrocarbyl group having a number averagemolecular weight of from 100 to 5000, preferably from 500 to 2500.

In some embodiments R³ is an optionally substituted aryl group oralkaryl group. For example R³ may be benzyl.

In some embodiments R³ is an optionally substituted alkyl or alkenylgroup. R³ may be an unsubstituted alkyl or alkenyl group. Suitably R³ isan alkyl or alkenyl group having from 1 to 200 carbon atoms.

In some embodiments R³ is an alkyl group or alkenyl group having 10 to36 carbon atoms.

In some embodiments R³ is a polyisobutenyl group, preferably apolyisobutenyl group having a molecular weight of from 100 to 5000,preferably from 300 to 4000, suitably from 450 to 2500, for example from500 to 2000 or from 600 to 1500.

In some embodiments R³ is an optionally substituted alkylene phenolmoiety and the tertiary amine R′R²R³N is the product of a Mannichreaction between an aldehyde, an optionally substituted phenol and anamine. Suitably the aldehyde is formaldehyde. The amine used to preparethe Mannich compound may be a monoamine and R³ would have the structure(A):

The amine used to prepare the Mannich compound may be a polyamine,including at least one tertiary amine group and R³ may have thestructure (B):

In structures (A) and (B) n is 0 to 4, preferably 1, each R^(x) is anoptionally substituted hydrocarbyl group, R^(y) is an optionallysubstituted alkyl, alkenyl or aryl group; and L is a linking group.

R^(y) and L may together form a heterocyclic group.

R^(y) is preferably an alkyl group, preferably an unsubstituted alkylgroup. R^(y) is suitably a C₁ to C₄ alkyl group.

Preferably L is an optionally substituted alkylene group, preferably analkylene group having 1 to 10, preferably 1 to 6 carbon atoms. Morepreferably L is an unsubstituted alkylene group, for example ethylene,propylene or butylene. Most preferably L is a propylene group.

In some preferred embodiments, the phenol includes an ortho-methylsubstituent and a further substituent R^(x) at the para-position.

In a preferred embodiment, n is 1 and the optionally substitutedhydrocarbyl substituent R is preferably para to the hydroxyl group.

The optionally substituted hydrocarbyl substituent R^(x) of the phenolcan have 6 to 400 carbon atoms, suitably 30 to 180 carbon atoms, forexample 10 or 40 to 110 carbon atoms. This hydrocarbyl substituent canbe derived from an olefin or a polyolefin.

The polyolefins which can form the hydrocarbyl substituent can beprepared by polymerizing olefin monomers by well known polymerizationmethods and are also commercially available.

Some preferred polyolefins include polyisobutylenes having a numberaverage molecular weight of 200 to 3000, in another instance of 400 to2500, and in a further instance of 400 or 500 to 1500.

In some embodiments the phenol may include a lower molecular weightalkyl substituent for example a phenol which carries one or more alkylchains having a total of less than 28 carbon atoms, preferably less than20 carbon atoms, more preferably less than 14 carbon atoms.

A monoalkyl phenol may be preferred, suitably having from 4 to 20carbons atoms, preferably 8 to 16 carbon atoms, for example a phenolhaving a C₁₂ alkyl substituent.

In some embodiments R³ may include an ether, amide or ester group.

In some embodiments R³ includes succinimide moiety. R³ may have theformula:

wherein R^(z) is an optionally substituted hydrocarbyl group and L is alinking group.

In some embodiments the optionally substituted hydrocarbyl substituentR^(z) can have 6 to 36 carbon atoms, preferably 8 to 22, for example 10to 18 or 16 to 18 carbon atoms.

In some embodiments the optionally substituted hydrocarbyl substituentR^(z) can have 6 to 400 carbon atoms, suitably 30 to 180 carbon atoms,for example 10 or 40 to 110 carbon atoms. This hydrocarbyl substituentcan be derived from an olefin or a polyolefin.

Some preferred polyolefins include polyisobutylenes having a numberaverage molecular weight of 200 to 3000, in another instance of 400 to2500, and in a further instance of 400 or 500 to 1500.

Preferably L is an optionally substituted alkylene group, preferably analkylene group having 1 to 10, preferably 1 to 6 carbon atoms. Morepreferably L is an unsubstituted alkylene group, for example ethylene,propylene or butylene. Most preferably L is a propylene group.

R³ may suitably be selected from an optionally substituted alkyl oralkenyl group having 1 to 10 carbon atoms; an optionally substitutedhydrocarbyl group having a molecular weight of 100 to 5000; anoptionally substituted alkylene phenol moiety and an optionallysubstituted alkylene succinimide group.

Suitable tertiary amine compounds for use as component (a) includesimple alkylamino and hydroxyalkylamino compounds; trialkylaminocompounds having a high molecular weight substituent; Mannich reactionproducts including a tertiary amine and substituted acylated amines oralcohols including a tertiary amine.

Simple alkylamino and hydroxyalkyl amino compounds are preferablycompounds of formula R¹R²R³N, wherein each of R′, R² and R³ is an alkylgroup or a hydroxyalkyl group. Each of R_(1, R) ² and R³ may be the sameor different. Suitably each of R¹, R² and R³ is independently selectedfrom an alkyl or hydroxyalkyl group having 1 to 10, preferably 1 to 6carbon atoms, for example 1 to 4 carbon atoms. Each of R¹, R² and R³ maybe independently selected from methyl, ethyl, propyl, butyl, pentyl,hexyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl,hydroxypentyl and hydroxyhexyl. Component (a) may be a trialkylamine, adialkylhydroxyalkylamine, a dihydroxyalkylalkylamine or atrihydroxyalkylamine. There are many different compounds of this typeand these will be known to the person skilled in the art.

In some embodiments the amine may include alkyl or hydroxyalkyl groupswhich have been reacted with an epoxide compound (for example ethyleneoxide or propylene oxide) to provide an ether.

Trialkylamino compounds having a high molecular weight substituentsuitable for use herein are typically polyalkene-substituted aminesincluding at least one tertiary amino group.

The polyalkene-substituted amines having at least one tertiary aminogroup of the present invention may be derived from an olefin polymer andan amine, for example ammonia, monoamines, polyamines or mixturesthereof. They may be prepared by a variety of methods such as thosedescribed and referred to in US 2008/0113890.

Suitably the polyalkene substituent of the polyalkene-substituted amineis derived from a polyisobutylene.

The amines that can be used to make the polyalkene-substituted amineinclude ammonia, monoamines, polyamines, or mixtures thereof, includingmixtures of different monoamines, mixtures of different polyamines, andmixtures of monoamines and polyamines (which include diamines). Theamines include aliphatic, aromatic, heterocyclic and carbocylic amines.Preferred amines are generally substituted with at least one hydrocarbylgroup having 1 to about 50 carbon atoms, preferably 1 to 30 carbonatoms. Saturated aliphatic hydrocarbon radicals are particularlypreferred.

The monoamines and polyamines suitably include at least one primary orsecondary amine group.

The number average molecular weight of the polyalkene-substituted aminescan range from 500 to 5000, or from 500 to 3000, for example from 1000to 1500.

Any of the above polyalkene-substituted amines which are secondary orprimary amines, may be alkylated to tertiary amines using alkylatingagents. Suitable alkylating agents and methods using these will be knownto the person skilled in the art.

Suitable Mannich reaction products having a tertiary amine for use ascomponent (a) are described in US 2008/0052985.

The Mannich reaction product having a tertiary amine group is preparedfrom the reaction of an optionally substituted hydrocarbyl-substitutedphenol, an aldehyde and an amine. The optionally substitutedhydrocarbyl-substituted phenol is suitably as previously describedherein.

Preferably the optionally substituted hydrocarbyl-substituted phenol isa polyisobutenyl-substituted phenol or a polyisobutenyl-substitutedcresol.

The aldehyde used to form the Mannich detergent can have 1 to 10 carbonatoms, and is generally formaldehyde or a reactive equivalent thereofsuch as formalin or paraformaldehyde.

The amine used to form the Mannich detergent can be a monoamine or apolyamine.

Examples of monoamines and polyamines are known to the person skilled inthe art. Preferred polyamines are polyethylene polyamines.

In especially preferred embodiments the amine used to form the Mannichdetergent comprises a diamine. Suitably it includes a primary orsecondary amine which takes part in the Mannich reaction and in additiona tertiary amine.

One preferred amine is dimethylaminopropylamine.

In preferred embodiments the Mannich detergent is the product directlyobtained from a Mannich reaction and comprising a tertiary amine. Forexample the amine may comprise a single primary or secondary amine whichwhen reacted in the Mannich reaction forms a tertiary amine which iscapable of being quaternised. Alternatively the amine may comprise aprimary or secondary amine capable of taking part in the Mannichreaction and also a tertiary amine capable of being quaternised. Howeverthe Mannich detergent may comprise a compound which has been obtainedfrom a Mannich reaction and subsequently reacted to form a tertiaryamine, for example a Mannich reaction may yield a secondary amine whichis then alkylated to form a tertiary amine.

Suitable preferred amines include dimethylamine and dibutylamine.

Substituted acylated amines or alcohols including a tertiary amine foruse as component (a) include the reaction product of an optionallysubstituted hydrocarbyl-substituted acylating agent and a compoundhaving an oxygen or nitrogen atom capable of condensing with saidacylating agent and further having a tertiary amino group.

The optionally substituted hydrocarbyl substituted acylating agent ispreferably a mono- or polycarboxylic acid (or reactive equivalentthereof) for example a substituted succinic, phthalic or propionic acid.

Preferred hydrocarbyl substituted acylating agents for use in thepreparation of component (i) are polyisobutenyl substituted succinicacid derivatives. Preferred compounds are those having a polyisobutenylgroup with a molecular weight of from 100 to 5000, preferably from 300to 4000, suitably from 450 to 2500, for example from 500 to 2000 or from600 to 1500.

In some preferred embodiments the tertiary amine comprises a compoundformed by the reaction of an optionally substitutedhydrocarbyl-substituted acylating agent and an amine of formula (II) or(III):

wherein R⁵ and R⁷ are the same or different alkyl, alkenyl or arylgroups having from 1 to 22 carbon atoms; A is a bond or is an alkylenegroup having from 1 to 20 carbon atoms; n is from 0 to 20; m is from 1to 5; and R⁴ is hydrogen or a C₁ to C₂₂ alkyl group.

The conditions of the above reaction are suitably selected to ensurethat there are no free acid groups present in the tertiary aminecomponent (a) that is formed. For example when a compound of formula(II) is reacted with a succinic acid derived acylating agent thereaction conditions or ratio of reactants are selected to ensure thatthe imide or diamide are formed. The monoamide is not formed. When acompound of formula (III) is reacted with a succinic acid derivedacylating agent the reaction conditions or ratio of reactants areselected to ensure that the diester is formed. The monoester is notformed.

When a compound of formula (II) is used, R⁸ is preferably hydrogen or aC₁ to C₁₈, suitably a C₁ to C₁₆ alkyl group. More preferably R⁸ isselected from hydrogen, methyl, ethyl, propyl, butyl and isomersthereof. Most preferably R⁸ is hydrogen.

When a compound of formula (III) is used, m is preferably 2 or 3, mostpreferably 2; n is preferably from 0 to 15, preferably 0 to 10, morepreferably from 0 to 5. Most preferably n is 0 and the compound offormula (III) is an alcohol.

Preferably the optionally substituted hydrocarbyl substituted acylatingagent is reacted with a diamine compound of formula (II).

R⁶ and R⁷ are the same or different alkyl, alkenyl or aryl groups havingfrom 1 to 22 carbon atoms. In some embodiments R⁶ and R⁷ may be joinedtogether to form a ring structure, for example a piperidine, imidazoleor morpholine moiety. Thus R⁶ and R⁷ may together form an aromaticand/or heterocyclic moiety. R⁶ and R⁷ may be branched alkyl or alkenylgroups. Each may be substituted, for example with a hydroxy or alkoxysubstituent.

Preferably each of R⁶ and R⁷ is independently a C₁ to C₁₆ alkyl group,preferably a C₁ to C₁₀ alkyl group. R⁶ and R⁷ may independently bemethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, or an isomerof any of these. Preferably R⁶ and R⁷ is each independently C₁ to C₄alkyl. Preferably R⁶ is methyl. Preferably R⁷ is methyl.

A is a bond or alkylene group having from 1 to 20 carbon atoms. A ispreferably an alkylene group having 1 to 12 carbon atoms, morepreferably 1 to 8 carbon atoms, for example 2 to 6 carbon atoms or 2 to5 carbon atoms. Most preferably A is an ethylene, propylene or butylenegroup, especially a propylene group.

Examples of compounds of formula (II) suitable for use herein will beknown to the person skilled in the art.

In some preferred embodiments the compound of formula (II) is selectedfrom dimethylaminopropylamine, N,N-diethyl-1,3-diaminopropane,N,N-dimethylethylenediamine, N,N-diethylethylenediamine mine,N,N-dibutylethylenediamine, or combinations thereof.

Examples of compounds of formula (III) suitable for use herein will beknown to the person skilled in the art.

In some preferred embodiments the compound of formula (III) is selectedfrom triisopropanolamine, 1-[2-hydroxyethyl]piperidine,2-[2-(dimethylamine)ethoxy]-ethanol, N-ethyldiethanolamine,N-methyldiethanolamine, N-butyldiethanolamine, N,N-diethylaminoethanol,N,N-dimethylaminoethanol, 2-dimethylamino-2-methyl-1-propanol, orcombinations thereof.

An especially preferred compound of formula (II) isdimethylaminopropylamine.

Further especially preferred tertiary amine compounds (a) are formed bythe reaction of a compound including a primary amine group and atertiary amine group and a polyisobutenyl-substituted succinic acid. Oneespecially preferred amine compound having a primary and a tertiaryamine group is dimethylaminopropylamine. The polyisobutenyl substituentpreferably has a molecular weight of from 300 to 2500, suitably from 500to 1500. Thus an especially preferred compound for use as component (a)is a polyisobutenyl-substituted succinimide prepared fromdimethylaminopropylamine.

Preferred tertiary amine compounds for use as component (a) includeN,N-dimethyl ethanolamine, dimethyloctadecylamine, N-methylN,N-ditallowamine, N,N-diethyl ethanolamine, triethylamine,tripropylamine and tributylamine.

Especially preferred tertiary amines for use as component (a) include N,N-dimethylethanolamine, N, N-diethylethanolamine, triethylamine andtributylamine.

Other suitable amine that may be used as component (a) include smallcyclic amines. These include for example compounds based on N-alkylheterocycles, suitably selected from pyrolidine, piperidine, morpholine,piperazine, pyrrole, imidazole and dihydropyrrole, pyridine, pyrimidine,isoxansole and oxazole. Suitable amine starting materials of this typeare described, for example, in the applicant's copending applicationPCT/GB2016/052312.

In some embodiments component (a) is selected from:

-   -   trialkyl amines in which each alkyl group has 1 to 6, preferably        1 to 4 carbons atoms;    -   dimethyl alkyl or alkenyl amines in which the alkyl or alkenyl        group has 6 to 36, preferably 10 to 30 carbon atoms;    -   tertiary amines in which each substituent is selected from        alkyl, hydroxylalkyl and hydroxyalkyloxyalkyl groups having 1 to        12, preferably 1 to 6 carbon atoms.

Preferred amines for use as component (a) are trialkylamines in whicheach alkyl group has 1 to 12, preferably 1 to 6 carbons atoms and inwhich each alkyl group may be hydroxyl substituted and/or substitutedwith an oxygen atom within the carbon chain.

Preferably component (a) is an amine of formula R¹R²R³N, wherein each ofR¹, R² and R³ is independently an unsubstituted alkyl group having 1 to6 carbon atoms, a hydroxy substituted alkyl group having 1 to 6 carbonatoms or a hydroxyalkyloxyalkyl group having 1 to 6 carbon atoms.

By hydroxyalkyloxyalkyl group we mean a group of formula HOR^(a)OR^(b)wherein each of R^(a) and R^(b) is an alkylene group. These may beformed by alkylation of a hydroxyalkyl substituent with an epoxide.

Most preferably component (a) is an amine of formula R¹R²R³N, whereineach of R¹, R² and R³ is independently an unsubstituted alkyl grouphaving 1 to 6 carbon atoms, or a hydroxy substituted alkyl group having1 to 6 carbon atoms.

Component (b) used to prepare the quaternary ammonium compound of thepresent invention in preferred embodiments is an acid activatedalkylating agent. Preferred acid-activated alkylating agents are epoxidecompounds.

Any suitable epoxide compound may be used. Suitable epoxide compoundsare those of formula:

wherein each of R⁹, R¹⁰, R¹¹, R¹² is independently selected fromhydrogen or an optionally substituted alkyl, alkenyl or aryl group.

In such embodiments R⁰ as shown in formula (I) is thus suitably a groupof formula:

Preferably at least one of R⁹, R¹⁰, R¹¹ and R¹² is hydrogen. Preferablyat least two of R⁹, R¹⁰, R¹¹ and R¹² are hydrogen. Most preferably threeof R⁹, R¹⁰, R¹¹ and R¹² are hydrogen. R⁹, R¹⁰, R¹¹ and R¹² may be allhydrogen.

In the structure above and the definitions which follow R⁹ and R¹⁰ areinterchangeable and thus when these groups are different eitherenantiomer or diastereomer may be used as component (b).

In the structure above and the definitions which follow R¹¹ and R¹² areinterchangeable and thus when these groups are different eitherenantiomer or diastereomer may be used as component (b).

Preferably R⁹ is hydrogen or an optionally substituted alkyl, alkenyl oraryl group, preferably having from 1 to 10, preferably from 1 to 4carbon atoms. Preferably R⁹ is hydrogen or an alkyl group. Mostpreferably R⁹ is hydrogen.

Preferably R¹⁰ is hydrogen or an optionally substituted alkyl, alkenylor aryl group, preferably having from 1 to 10 carbon atoms. For exampleR¹⁰ may be benzyl.

In some preferred embodiments R¹⁰ is an optionally substituted arylgroup. For example R¹⁰ may be phenyl.

In some preferred embodiments R¹⁰ is an optionally substituted alkyl oralkenyl group. Suitably R¹⁰ is an alkyl group, for example anunsubstituted alkyl group. R¹⁰ may be an alkyl group having 1 to 12, forexample 1 to 8 or 1 to 4 carbon atoms.

Preferably R¹⁰ is hydrogen or an alkyl group. Most preferably R¹⁰ ishydrogen.

Preferably R¹¹ is hydrogen or an optionally substituted alkyl, alkenylor aryl group, preferably having from 1 to 10, preferably from 1 to 4carbon atoms. Preferably R¹¹ is hydrogen or an alkyl group. Mostpreferably R¹¹ is hydrogen.

Preferably R¹² is hydrogen or an optionally substituted alkyl, alkenylor aryl group.

In some preferred embodiments R¹² is an optionally substituted arylgroup. For example R¹² may be phenyl.

In some preferred embodiments R¹² is an optionally substituted alkyl oralkenyl group. R¹² may be an alkyl group, for example an unsubstitutedalkyl group. R¹² may be an alkyl group having 1 to 50 carbon atoms,preferably from 1 to 30 carbon atoms, suitably 1 to 20 carbon atoms,preferably from 1 to 12 carbon atoms, for example from 1 to 8 or from 1to 4 carbon atoms.

In some embodiments R¹² is an alkyl group having 6 to 20 carbon atoms,preferably from 8 to 16 carbon atoms.

In some embodiments R¹² is hydrogen.

In some preferred embodiments R¹² is the moiety CH₂OR¹³ or CH₂OCOR¹⁴wherein each of R¹³ and R¹⁴ may be an optionally substituted alkyl,alkenyl or aryl group.

R¹³ is preferably an optionally substituted alkyl or aryl group,preferably having from 1 to 30 carbon atoms, preferably from 1 to 20carbon atoms, suitably from 1 to 12 carbon atoms. When R¹³ is an alkylgroup it may be straight-chained or branched. In some embodiments it isbranched. R¹³ may be an optionally substituted phenyl group.

In one embodiment R¹³ is a 2-methyl phenyl group. In another embodimentR¹³ is CH₂C(CH₂CH₃)CH₂CH₂CH₂CH₃.

R¹⁴ may be an optionally substituted alkyl, alkenyl or aryl group.

R¹⁴ is preferably an optionally substituted alkyl or aryl group,preferably having from 1 to 30 carbon atoms, preferably from 1 to 20carbon atoms, suitably from 1 to 12 carbon atoms. When R¹⁴ is an alkylgroup it may be straight-chained or branched. In some preferredembodiments it is branched. R¹⁴ may be an optionally substituted phenylgroup.

In one embodiment R¹⁴ is C(CH₃)R² wherein each R is an alkyl group. TheR groups may be the same or different.

Component (b) is preferably an epoxide. The present invention thereforeprovides a quaternary ammonium compound which is the reaction productof:

(a) a tertiary amine of formula R¹R²R³N;

(b) an epoxide; and

(c) a compound of formula HOOCXCOO(R⁴O)R⁵ wherein R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is 0 or a positive integer, providedthat n is not 0 when R⁵ is hydrogen.

Preferred epoxide compounds for use as component (b) include styreneoxide, ethylene oxide, propylene oxide, butylene oxide, epoxyhexane,octene oxide, stilbene oxide and other alkyl and alkenyl epoxides having2 to 50 carbon atoms.

Other suitable epoxide compounds include glycidyl ethers and glycidylesters, for example gylcidyl 2 methyl phenyl ether and the glycidylester of versatic acid.

Suitably component (b) may be selected from styrene oxide, ethyleneoxide, propylene oxide, butylene oxide, epoxyhexane, octene oxide,stilbene oxide, 2-ethylhexyl glycidyl ether, 1,2-epoxydodecane and otheralkyl and alkenyl epoxides having 2 to 50 carbon atoms.

Preferably component (b) is selected from styrene oxide, propyleneoxide, butylene oxide, and 2-ethylhexyl glycidyl ether.

More preferably component (b) is selected from propylene oxide, butyleneoxide and 2-ethylhexyl glycidyl ether.

The quaternary ammonium salt of the present invention includes an anionof formula —OOCXCOO(R⁴O)_(n)R⁵.

Suitably the quaternary ammonium salt is prepared by reaction of (a) aquaternary amine; (b) an epoxide; and (c) an acid of formulaHOOCXCOO(R⁴O)_(n)R^(5.)

The compound of formula. —IOOCXCOO(R⁴O)_(n)R⁵ is suitably a half esterwhich is the reaction product of an optionally substituted dicarboxylicacid or anhydride thereof and an alcohol of formula HO(R⁴O)_(n)R⁵.

In some embodiments the dicarboxylic acid or anhydride is unsubstituted.In preferred embodiments the additive is prepared from a hydrocarbylsubstituted dicarboxylic acid or an anhydride thereof.

Suitable dicarboxylic acids include maleic acid, glutaric acid, fumaricacid, oxalic acid, malonic acid, pimelic acid, suberic acid, adipicacid, phthalic acid, succinic acid, azelaic acid, sebacic acid anddimerised fatty acids.

In one embodiment component (c) is the reaction product of an optionallysubstituted polycarboxylic acid or anhydride thereof selected frompyromellitic acid, malonic acid, sebacic acid and succinic acid.Suitably component (c) is an optionally substituted succinic acid or ananhydride thereof.

In some embodiments the compound of formula HOOCXCOO(R⁴O)R⁵ (component(c)) is prepared from a dimerised fatty acid. Such compounds are formedfrom the dimerization of unsaturated fatty acids, for exampleunsaturated fatty acids having 6 to 50, suitably 8 to 40, preferably 10to 36, for example 10 to 20 carbon atoms, or 16 to 20 carbon atoms.

Such dimerised fatty acids may have 12-100 carbon atoms, preferably16-72 carbon atoms such as 20-40 carbon atoms for example 32-40 carbonatoms.

These compound are well known in the art, particularly for their use ascorrosion inhibitors. Particularly preferred dimerised fatty acids aremixtures of C36 dimer acids such as those prepared by dimerising oleicacid, linoleic acid and mixtures comprising oleic and linoleic acid, forexample, tall oil fatty acids.

The quatemary ammonium compound of formula (i) includes a linking groupX. Preferably X includes a hydrocarbyl substituent. Preferably X is anoptionally substituted arylene or alkylene group.

In some embodiments component (c) is prepared from phthalic acid or ananhydride thereof, having the formula (A1) or (A2):

wherein each of R^(p), R^(q), R^(r) and R^(s) is independently hydrogenor an optionally substituted hydrocarbyl group.

Preferably each is hydrogen or an optionally substituted alkyl oralkenyl group. Preferably three of R^(p), R^(q), R^(r) and R^(s) arehydrogen and the other is an optionally substituted C₁ to C₅₀₀ alkyl oralkenyl group, preferably a C₂ to C₁₀₀ alkyl or alkenyl group,preferably a C₆ to C₅₀ alkyl or alkenyl group, preferably a C₈ to C₄₀alkyl or alkenyl group, more preferably a C₁₀ to C₃₆ alkyl or alkenylgroup, preferably a C₁₂ to C₂₂ alkyl or alkenyl group, suitably a C₁₆ toC₂₈ alkyl or alkenyl group, for example a C₂₀ to C₂₄ alkyl or alkenylgroup. The alkyl or alkenyl group may be straight chain or branched.Preferably R^(p), R^(q) and R^(s) are hydrogen and R^(r) is anoptionally substituted alkyl or alkenyl group.

X in formula (I) is preferably an optionally substituted hydrocarbylenegroup. Preferably X is an optionally substituted alkylene group.Preferably X is a substituted alkylene group.

Suitably X is an alkyl or alkenyl substituted alkylene group.

Preferably X is an alkyl substituted alkylene group.

Preferably X is an alkyl substituted alkylene group wherein the alkylenegroup was 1 to 10, preferably 1 to 6, suitably 1 to 4, preferably 2 or3, and most preferably 2 carbon atoms in the alkylene chain.

In some preferred embodiments X is CH₂CHR or CHRCH₂ wherein R is anoptionally substituted hydrocarbyl group.

Preferably component (c) used to prepare the quaternary ammonium salt ofthe present invention is the reaction product of an optionallysubstituted succinic acid or anhydride thereof of formula (A3) or (A4):

wherein R is hydrogen or an optionally substituted hydrocarbyl group.Preferably R⁴ is an optionally substituted alkyl or alkenyl group.

In some embodiments R is an optionally substituted C₁ to C₅₀₀ alkyl oralkenyl group, preferably a C₂ to C₁₀₀ alkyl or alkenyl group,preferably a C₆ to C₅₀ alkyl or alkenyl group, preferably a C₈ to C₄₀alkyl or alkenyl group, more preferably a C₁₀ to C₃₈ alkyl or alkenylgroup, preferably a C₁₆ to C₃₆ alkyl or alkenyl group, suitably a C₁₈ toC₃₂ alkyl or alkenyl group.

R may be substituted with one or more groups selected from halo (e.g.chloro, fluoro or bromo), nitro, hydroxy, mercapto, sulfoxy, amino,nitryl, acyl, carboxy, alkyl (e.g. C₁ to C₄ alkyl), alkoxyl (e.g. C₁ toC₄ alkoxy), amido, keto, sulfoxy and cyano.

Preferably R is an unsubstituted alkyl or alkenyl group. The substitutedsuccinic acid or anhydrides may suitably be prepared by reacting maleicanhydride with an alkene.

In some embodiments the R has a molecular weight of from 100 to 5000,preferably from 300 to 4000, suitably from 450 to 2500, for example from500 to 2000 or from 600 to 1500.

In some embodiments the substituted succinic acid or anhydride thereofmay comprise a mixture of compounds including groups R of differentlengths. In such embodiments any reference to the molecular weight ofthe group R relates to the number average molecular weight for themixture.

In some embodiments R is a polyisobutenyl group, preferably having anumber average molecular weight of from 100 to 5000, preferably from 200to 2000, suitably from 220 to 1300, for example from 240 to 900.

In some embodiments R is a polyisobutenyl group having a number averagemolecular weight of from 400 to 700.

In some embodiments R is a polyisobutenyl group having a number averagemolecular weight of from 180 to 400.

In some embodiments R is a polyisobutenyl group having a number averagemolecular weight of from 800 to 1200.

In some embodiments R is an alkyl or alkenyl group having 6 to 40 carbonatoms, preferably 10 to 38 carbon atoms, more preferably 16 to 36 carbonatoms, suitably 18 to 26 carbon atoms, for example 20 to 24 carbonatoms.

In some embodiments R may be the residue of an internal olefin. In suchembodiments the compound of formula (A3) or (A4) is suitably obtained bythe reaction of maleic acid with an internal olefin.

An internal olefin as used herein means any olefin containingpredominantly a non-alpha double bond that is a beta or higher olefin.Preferably such materials are substantially completely beta or higherolefins, for example containing less than 10% by weight alpha olefin,more preferably less than 5% by weight or less than 2% by weight.Typical internal olefins include Neodene 1518IO available from Shell.

Internal olefins are sometimes known as isomerised olefins and can beprepared from alpha olefins by a process of isomerisation known in theart, or are available from other sources. The fact that they are alsoknown as internal olefins reflects that they do not necessarily have tobe prepared by isomerisation.

Component (c) is the reaction product of a succinic acid or anhydride offormula (A3) or (A4) and an alcohol of formula H—(OR⁴)_(n)—OR⁵; whereinR is an alkyl or alkenyl group having 6 to 36 carbon atoms or apolyisobutenyl group having a number average molecular weight of from200 to 1300.

In some especially preferred embodiments component (c) is prepared froma succinic acid or anhydride having a C₁₀ to C₃₀, preferably a C₂₀ toC₂₄ alkyl or alkenyl group.

Component (c) may have the formula (B1) or (B2):

Such a compound may be prepared by the reaction of a hydrocarbylsubstituted succinic acid or anhydride with an alcohol of formulaHO(R⁴O)_(n)R⁵.

Preferably the acid/anhydride and the alcohol are reacted in a molarratio of from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferablyfrom 2:1 to 1:2, for example from 1.5:1 to 1:1.5.

Most preferably the acid/anhydride and the alcohol are reacted in anapproximately 1:1 molar ratio, for example from 1.2:1 to1:1.2.

Suitably n is from 0 to 30, preferably from 0 to 20, suitably from 1 to16; R⁴ is an alkylene group having 1 to 12, preferably 1 to 6, morepreferably 2 or 3 carbon atoms; and R⁵ is hydrogen or a C₁ to C₄₀,preferably a C₆ to C₃₀, more preferably a C₁₀ to C₂₀ alkyl group;provided n is not 0 when R⁵ is hydrogen.

R⁵ is an optionally substituted hydrocarbyl group.

In some embodiments n is 0 and the additive of the invention may beformed from an alcohol of formula R⁵OH.

In such embodiments R⁵ is suitably an optionally substituted alkyl,alkenyl or aryl group, preferably having from 1 to 60, preferably from10 to 40 carbon atoms. Preferably R⁵ is an optionally substituted alkylgroup. In some embodiments R⁵ is a hydroxy substituted alkyl group.

In some preferred embodiments R⁵ is an unsubstituted alkyl group. Thealkyl group may be straight chained or branched. In some embodiments R⁵is an optionally substituted alkyl group having 4 to 40, preferably 6 to30, more preferably 10 to 20 carbon atoms.

In some embodiments n is 0 and component (c) is prepared from a C₆ toC₃₆, preferably a C₈ to C₃₀, more preferably a C₁₀ to C₂₀ optionallysubstituted alcohol.

In one embodiment component (c) is an ester of tetradecanol.

Suitable alcohols of formula R⁵OH for use herein include benzyl alcohol,tetradecanol, butanol, 2-butanol, isobutanol, octanol, 2-ethylhexanol,hexanol, cyclohexanol, cyclooctanol, 2-propylheptanol, 2-ethyl-1-butanoland isopropanol.

Suitable alcohols of formula R⁵OH for use herein are butanol and2-ethylhexanol.

In some embodiments n is not 0 and the quaternary ammonium salt maysuitably be formed from an alcohol of formula HO(R⁴O)_(n)R⁵.

R⁵ is hydrogen or an optionally substituted hydrocarbyl group.

When R⁵ is hydrogen component (c) is suitably an ester of an alkyleneglycol or a polyalkylene glycol.

When R⁵ is not hydrogen, component (c) may be formed by reaction of theoptionally substituted dicarboxylic acid with an alkylene glycol orpolyalkylene glycol which is subsequently reacted to form an ether or acompound of formula HO(R⁴O)_(n)R⁵ may be reacted with the optionallysubstituted dicarboxylic acid.

R⁴ is an optionally substituted alkylene group.

In some embodiments the alcohol of formula H—(OR)_(n)—OH has more than 2hydroxy groups and the group R is a hydroxyl substituted alkylene group.Such a group may have 1, 2 or more hydroxyl groups.

For example in some embodiments the alcohol H—(OR)_(n)—OH may beglycerol, penterythritol or trimethylolpropane.

Preferably R⁴ is an unsubstituted alkylene group.

Preferably R⁴ is an optionally substituted alkylene group having 1 to 50carbon atoms, preferably 1 to 40 carbon atoms, preferably 1 to 30 carbonatoms, more preferably 1 to 20 carbon atoms, suitably 1 to 10 carbonatoms, for example 2 to 6 or 2 to 4 carbon atoms.

Preferably R⁴ is an unsubstituted alkylene group having 1 to 50 carbonatoms, preferably 1 to 20, more preferably 1 to 10, suitably 2 to 6, forexample 2 to 4 carbon atoms. R⁴ may be straight chained or branched.

Suitably R⁴ may be an ethylene, propylene, butylene, pentylene, orhexylene group. When R⁴ has more than 2 carbon atoms any isomer may bepresent. Preferably R⁴ is an ethylene or a propylene group, mostpreferably a propylene group.

In some embodiments in which n is 1, R⁴ may be a group of formula(CH₂)_(x) wherein x is from 2 to 12, preferably from 2 to 6.

In some embodiments in which n is 1, R⁴ is a straight chain or branchedalkylene group and the alcohol is selected from ethylene glycol,propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 1,6-hexanediol and neopentyl glycol.

In some preferred embodiments R⁴ is preferably CR^(a)R^(b)CR^(c)R^(d)and the polyhydric alcohol has the formulaH—(OCR^(a)R^(b)CR^(c)R^(d))_(n)OH wherein each of R^(a), R^(b), R^(c)and R^(d) is independently hydrogen or an optionally substituted alkylgroup. Preferably each R^(a), R^(b), R^(c) and R^(d) is independentlyselected from hydrogen or an optionally substituted alkyl group having 1to 20, preferably 1 to 12, more preferably 1 to 4, for example 1 to 2carbon atoms.

Preferably each of R^(a), R^(b), R^(c) and R^(d) is independentlyselected from hydrogen and an unsubstituted alkyl group, preferablyhaving 1 to 20 carbon atoms, suitably 1 to 12 carbon atoms, preferably 1to 4 atoms, for example 1 or 2 carbon atoms. Preferably at least two ofR^(a), R^(b), R^(c) and R^(d) is hydrogen, more preferably at leastthree of R^(a), R^(b), R^(c) and R^(d) is hydrogen.

In some embodiments R^(a), R^(b), R^(c) and R^(d) are all hydrogen and Ris an ethylene group CH₂CH₂.

In some embodiments three of R^(a), R^(b), R^(c), and R^(d) is hydrogenand the other is an unsubstituted alkyl group having 1 to 12, preferably1 to 4, suitably 1 to 2, and most preferably 1 carbon atoms.

In some embodiments the polyhydric alcohols used to prepare component(c) are prepared from epoxides, preferably terminal epoxides.

R⁴ may comprise a mixture of isomers. For example when R⁴ is propylene,the polyhydric alcohol may include moieties —CH₂CH(CH₃)— and—CH(CH₃)CH₂— in any order within the chain.

R⁴ may comprise a mixture of different groups for example ethylene,propylene or butylene units. Block copolymer units are preferred in suchembodiments.

R⁴ is preferably an ethylene, propylene or butylene group. R⁴ may be ann-propylene or n-butylene group or an isopropylene or isobutylene group.For example R⁴ may be —CH₂CH₂—, —CH₂CH(CH₃)—, —CH₂C(CH₃)₂,—CH(CH₃)CH(CH₃)— or —CH₂CH(CH₂CH₃)—.

Preferably R⁴ is ethylene or propylene. More preferably R⁴ is —CH₂CH₂—or —CH(CH₃)CH₂—. Most preferably R⁴ is —CH(CH₃)CH₂—.

In some embodiments n is at least 1. Preferably n is from 1 to 100,preferably from 1 to 50, more preferably from 1 to 30, more preferablyfrom 1 to 24, preferably from 1 to 20, suitably from 1 to 16, preferablyfrom 1 to 14.

In some embodiments n is from 4 to 10, for example from 6 to 8.

In some embodiments n is from 1 to 6, suitably from 2 to 5, for example3 or 4.

In some embodiments n is from 8 to 16, for example from 11 to 14.

In some embodiments component (c) is prepared from a polyhydric alcoholof formula HO(R⁴O)H or an ether thereof of formula HO(R⁴O)_(n)R⁵.

Preferably the acid/anhydride and the alcohol are reacted in a molarratio of from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferablyfrom 2:1 to 1:2, for example from 1.5:1 to 1:1.5.

Most preferably the acid/anhydride and the alcohol are reacted in anapproximately 1:1 molar ratio, for example from 1.2:1 to 1:1.2.

In some embodiments the polyhydric alcohol may be a polypropylene glycolhaving a number average molecular weight of 425.

In some embodiments the polyhydric alcohol may be selected fromtriethylene glycol, tetraethyelene glycol, propylene glycol, dipropyleneglycol and tripropylene glycol.

In some embodiments the polyhydric alcohol is selected from ethyleneglycol, propylene glycol and oligomers or polymers thereof.

In some embodiments the polyhydric alcohol may be a polypropylene glycolhaving a number average molecular weight of 725.

The skilled person will appreciate that commercial sources of alcoholsof formula H—(OR⁴)_(n)—OH will often contain mixtures of compounds, forexample in which n may be between 6 and 10.

Commercial sources of substituted succinic acids and anhydrides may alsocontain mixtures of compounds, for example including different compoundswith substituents having 20 to 24 carbon atoms.

In some preferred embodiments R⁵ is hydrogen.

In some embodiments R⁵ is hydrogen, n is 1, and R is a straight chain orbranched alkylene group. In such embodiments the alcohol of formulaHO(R⁴O)_(n)R⁵ is selected from ethylene glycol, propylene glycol,1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol,1,6-hexanediol and neopentyl glycol.

In some embodiments R⁵ is not hydrogen, n is not 0 and the additive ofthe invention is prepared from an ether of a polyhydric alcohol, forexample an ether of a polyethylene glycol, a polypropylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, dipropyleneglycol or tripropylene glycol.

In some embodiments in which n is not 0, R⁵ is an optionally substitutedalkyl, alkenyl or aryl group, suitably an optionally substituted alkylor alkenyl group. Preferably R⁵ has from 4 to 50 carbon atoms,preferably 4 to 40 carbon atoms, more preferably from 10 to 30 carbonatoms. R⁵ may be straight chain or branched. Preferably R⁵ is straightchain.

In some embodiments R⁵ is a substituted alkyl or alkenyl group, suitablya substituted alkyl group. Suitably substituents are hydroxy and estergroups.

Suitably R⁵ is an unsubstituted alkyl or alkenyl group. Preferably R⁵ isan alkyl group, preferably an unsubstituted alkyl group.

Suitably R⁵ is selected from hydrogen, and an alkyl group having from 1to 40, preferably 6 to 30, more preferably 10 to 20 carbon atoms.

In some embodiments n is from 10 to 40, preferably 15 to 30, morepreferably 20 to 25; R² is ethylene or propylene, most preferablypropylene; and R⁵ is a C₆ to C₃₀, preferably a C₁₀ to C₂₀ alkyl group.

In some embodiments component (c) is the reaction product of anoptionally substituted polycarboxylic acid or anhydride thereof selectedfrom pyromellitic acid, malonic acid, sebacic acid and succinic acid;and an alcohol of formula HO(R⁴O)_(n)R⁵, the alcohol being selectedfrom:

-   -   ethylene glycol, propylene glycol and oligomers or polymers        thereof; alkane diols having 1 to 12, preferably 3 to 6 carbon        atoms; sugar alcohols or ethers thereof; and    -   alkanols having 1 to 30, preferably 6 to 25 carbon atoms.

In some embodiments component (c) is the reaction product of anoptionally substituted polycarboxylic acid or anhydride thereof selectedfrom pyromellitic acid and succinic acid; and an alcohol of formulaHO(R⁴O)_(n)R⁵ wherein the alcohol is selected from:

-   -   ethylene glycol, diethylene glycol, triethylene glycol,        tetraethylene glycol, propylene glycol, dipropylene glycol,        tripropylene glycol, tetrapropylene glycol, trehalose,        1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol,        1,6-hexanediol, neopentyl glycol, a polyethylene or        polypropylene glycol having a number average molecular weight of        300 to 1200; or a C₁ to C₃₀ ether thereof; and    -   benzyl alcohol, tetradecanol, butanol, 2-butanol, isobutanol,        octanol, 2-ethylhexanol, hexanol, cyclohexanol, cyclooctanol,        2-propylheptanol, 2-ethyl-1-butanol and isopropanol.

In some embodiments component (c) is the reaction product of a succinicacid or anhydride of formula (A3) or (A4) and an alcohol of formulaHO(R⁴O)_(n)R⁵; wherein R² is an alkyl or alkenyl group having 6 to 36carbon atoms or a polyisobutenyl group having a number average molecularweight of from 200 to 1300; wherein the alcohol of formula HO(R⁴O)_(n)R⁵is selected from:

-   -   ethylene glycol, diethylene glycol, triethylene glycol,        tetraethylene glycol, propylene glycol, dipropylene glycol,        tripropylene glycol, tetrapropylene glycol, trehalose, sorbitol,        glycerol, pentaerythritol, trimethylolpropane, 1,3-propanediol,        1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol,        neopentyl glycol and a polyethylene or polypropylene glycol        having a number average molecular weight of 300 to 1200; or a C₆        to C₂₄ ether thereof; and    -   benzyl alcohol, tetradecanol, butanol, 2-butanol, isobutanol,        octanol, 2-ethylhexanol, hexanol, cyclohexanol, cyclooctanol,        2-propylheptanol, 2-ethyl-1-butanol and isopropanol.

In some embodiments component (c) used to prepare the quaternaryammonium salt of the present invention is the reaction product of asuccinic acid or anhydride thereof having an alkyl or alkenylsubstituent having 6 to 36 carbon atoms and a polypropylene glycol (or aC₁ to C₃₆ alkyl ether thereof) having a number average molecular weightof 300 to 800.

In some embodiments component (c) is the reaction product of a succinicacid or anhydride thereof having an alkyl or alkenyl substituent having6 to 36 carbon atoms and a polyhydric alcohol (or a C₁ to C₃₆ alkylether thereof) selected from ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, dipropyleneglycol, tripropylene glycol and tetrapropylene glycol.

In some embodiments component (c) is the reaction product of a succinicacid or anhydride thereof having an alkyl or alkenyl substituent having6 to 36 carbon atoms and a polyhydric alcohol (or a C₁ to C₃₆ alkylether thereof) selected from glycerol, pentaerythritol andtrimethyolpropane.

In some embodiments component (c) is the reaction product of a succinicacid or anhydride having a C₆ to C₃₆, preferably a C₁₀ to C₃₀, morepreferably a C₂₀ to C₂₄ alkyl or alkenyl substituent and a polyethyleneor polypropylene glycol (or a C₁ to C₃₆ alkyl ether thereof) having 4 to16, preferably 6 to 8 alkoxy groups.

In some embodiments component (c) is the reaction product of a succinicacid or anhydride having a C₁₀ to C₃₀, preferably a C₂₀ to C₂₄ alkyl oralkenyl substituent and an alcohol of formula R⁵OH wherein R⁵ is a C₆ toC₃₀, preferably a C₁₀ to C₂₀ alkyl group.

In some embodiments component (c) is the reaction product of a succinicacid or anhydride thereof having an alkyl or alkenyl substituent having6 to 36 carbon atoms and a polyethylene glycol (or a C₁ to C₃₈ alkylether thereof) having a number average molecular weight of 200 to 800.

In some embodiments component (c) is the reaction product of apolyisobutenyl substituted succinic acid or anhydride thereof having aPIB substituent with a number average molecular weight of 200 to 2500and a polypropylene glycol (or a C₁ to C₃₆ alkyl ether thereof) having anumber average molecular weight of 300 to 800.

In some embodiments component (c) is the reaction product of apolyisobutenyl substituted succinic acid or anhydride thereof having aPIB substituent with a number average molecular weight of 200 to 2500and a polyhydric alcohol (or a C₁ to C₃₆ alkyl ether thereof) selectedfrom ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, propylene glycol, dipropylene glycol, tripropyleneglycol and tetrapropylene glycol.

In some embodiments component (c) is the reaction product of apolyisobutenyl substituted succinic acid or anhydride thereof having aPIB substituent with a number average molecular weight of 200 to 2500and a polyhydric alcohol (or a C₁ to C₃₆ alkyl ether thereof) selectedfrom glycerol, pentaerythritol and trimethyolpropane.

In some embodiments component (c) is a the reaction product ofpolyisobutenyl substituted succinic acid or anhydride thereof having aPIB substituent with a number average molecular weight of 200 to 2500and a polyethylene glycol (or a C₁ to C₃₆ alkyl ether thereof) having anumber average molecular weight of 200 to 800.

In some embodiments component (c) is the reaction product of apolyisobutenyl substituted succinic acid or anhydride thereof having aPIB substituent with a number average molecular weight of 200 to 2500 apolyethylene or polypropylene glycol (or a C₁ to C₃₈ alkyl etherthereof) having 4 to 16, preferably 6 to 8 alkoxy groups.

For avoidance of doubt component (c) may comprise a mixture ofcompounds. Compounds that may be present include mixtures formed byreacting a mixture of different polyhydric alcohols with apolycarboxylic acid and/or mixtures formed by reacting a polyhydricalcohol with a mixture of polycarboxylic acids and/or compounds formedby reacting a mixture of polyhydric alcohols with a mixture ofcarboxylic acids. Such mixtures may also include mixtures of initiallypure fully formed ester compounds.

In an especially preferred embodiment component (c) is the reactionproduct of a succinic acid or anhydride having a C₂₀ to C₂₄ alkyl oralkenyl substituent and an alcohol selected from polypropylene glycolhaving a number average molecular weight of 300 to 800, 2-ethylhexanoland butanol.

In preferred embodiments the quaternary ammonium compound of the presentinvention is the reaction product of:

-   -   (a) a tertiary amine of formula R¹R²R³N wherein each of, R¹, R²        and R³ is independently an optionally substituted alkyl group        having 1 to 12 carbon atoms;    -   (b) an epoxide selected from styrene oxide, ethylene oxide,        propylene oxide, butylene oxide, epoxyhexane, octene oxide,        stilbene oxide, 2-ethylhexyl glycidyl ether, 1,2-epoxydodecane        and other alkyl and alkenyl epoxides having 2 to 50 carbon        atoms; and    -   (c) a compound of formula HOOCXCOO—(R⁴O)_(n)—R⁵ wherein X is        CH₂CHR or CHRCH₂ wherein R is an optionally substituted        hydrocarbyl group; and n is more than 1, R⁴ is an ethylene or        propylene group and R⁵ is hydrogen; or n is 0 or and R⁵ is a C₁        to C₂₀ alkyl group.

In more preferred embodiments the quaternary ammonium compound of thepresent invention is the reaction product of:

-   -   (a) a tertiary amine of formula R¹R²R³N wherein each of, R¹, R²        and R³ is independently an alkyl or hydroxyalkyl group having 1        to 6 carbon atoms;

(b) an epoxide selected from propylene oxide, butylene oxide and2-ethylhexyl glycidyl ether; and

(c) a compound of formula HOOCXCOO—(R⁴O)_(n)—R⁵ which is the reactionproduct of a succinic acid or anhydride having a C₂₀ to C₂₄ alkyl oralkenyl substituent and an alcohol selected from polypropylene glycolhaving a number average molecular weight of 300 to 800, 2-ethylhexanoland butanol.

According to a third aspect of the present invention there is provided acomposition comprising a quaternary ammonium compound of formula (I):

wherein R⁰, R¹, R² and R³ is each independently an optionallysubstituted hydrocarbyl group, X is a linking group, R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is 0 or a positive integer, providedthat n is not 0 when R⁵ is hydrogen.

Preferred features of the third aspect are as defined in relation to thefirst and second aspects.

In some embodiments the composition of the third aspect is an additivecomposition comprising a quaternary ammonium salt of the first aspectand a diluent or carrier.

The additive composition may be an additive composition for lubricatingoil.

Preferably the additive composition is an additive composition for afuel composition, preferably a diesel fuel composition.

The quaternary ammonium compound is suitably present in the additivecomposition in an amount of from 1 to 99 wt %, for example from 1 to 75wt %.

The additive composition may comprise a mixture of two or morequaternary ammonium compounds of the present invention. In suchembodiments the above amounts suitably refer to the total amount of allsuch compounds present in the composition.

The additive composition may include one or more further additives.These may be selected from antioxidants, dispersants, detergents, metaldeactivating compounds, wax anti-settling agents, cold flow improvers,cetane improvers, dehazers, stabilisers, demulsifiers, antifoams,corrosion inhibitors, lubricity improvers, dyes, markers, combustionimprovers, metal deactivators, odour masks, drag reducers andconductivity improvers.

In some preferred embodiments the additive composition includes one ormore further nitrogen-containing detergents.

The third aspect of the present invention may provide a fuel orlubricating oil composition comprising a quaternary ammonium salt of thefirst aspect.

In some embodiments the present invention provides a lubricatingcomposition comprising an oil of lubricating viscosity and as anadditive a quaternary ammonium salt of formula (I):

wherein R⁰, R¹, R² and R³ is each independently an optionallysubstituted hydrocarbyl group, X is a linking group, R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is 0 or a positive integer, providedthat n is not 0 when R⁵ is hydrogen.

In some preferred embodiments the third aspect of the present inventionprovides a fuel composition comprising as an additive a quaternaryammonium salt of formula (I):

wherein R⁰, R¹, R² and R³ is each independently an optionallysubstituted hydrocarbyl group, X is a linking group, R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is 0 or a positive integer, providedthat n is not 0 when R⁵ is hydrogen.

The present invention may further provide a method of preparing a fuelcomposition, the method comprising preparing a quaternary ammonium saltof the first aspect, and mixing the quaternary ammonium salt into thefuel.

The fuel composition of the present invention is preferably a dieselfuel composition.

Suitably the quaternary ammonium salt additive is present in the dieselfuel composition in an amount of at least 0.1 ppm, preferably at least 1ppm, more preferably at least 5 ppm, suitably at least 10 ppm,preferably at least 20 ppm, for example at least 30 ppm or at least 50ppm.

Suitably the quaternary ammonium salt additive is present in the dieselfuel composition in an amount of less than 10000 ppm, preferably lessthan 1000 ppm, preferably less than 500 ppm, preferably less than 300ppm, for example less than 250 ppm.

In some embodiments the quaternary ammonium salt additive is present inthe diesel fuel composition in an amount of suitably less than 200 ppm,for example less than 150 ppm.

Suitably the quaternary ammonium salt additive is present in the dieselfuel in an amount of from 80 to 130 ppm.

In this specification any reference to ppm is to parts per million byweight.

The diesel fuel compositions of the present invention may comprise amixture of two or more quaternary ammonium salt additives. In suchembodiments the above amounts refer to the total amounts of all suchadditives present in the composition.

The use of mixtures may arise due to the availability of startingmaterials or a particular mixture may be deliberately selected to use inorder to achieve a benefit. For example, a particular mixture may leadto improvements in handling, a general improvement in performance or asynergistic improvement in performance.

In this specification any reference to “an additive” or “the additive”of the invention includes embodiments in which a single additivecompound is present and embodiments in which two or more additivecompounds are present. In embodiments in which two or more compounds arepresent the mixtures may be present due to a mixture of startingmaterials being used to prepare the additive compounds (e.g. a mixtureof polyhydric alcohols and/or a mixture of polycarboxylic acids and/or amixture of tertiary amines and/or a mixture of quaternising agents).Alternatively and/or additionally two or more pre-formed compounds offormula (I) may be mixed into a composition, for example a fuel orlubricating composition.

The quaternary ammonium salt additives may be added to diesel fuel atany convenient place in the supply chain. For example, the additives maybe added to fuel at the refinery, at a distribution terminal or afterthe fuel has left the distribution terminal. If the additive is added tothe fuel after it has left the distribution terminal, this is termed anaftermarket application. Aftermarket applications include suchcircumstances as adding the additive to the fuel in the delivery tanker,directly to a customer's bulk storage tank, or directly to the enduser's vehicle tank. Aftermarket applications may include supplying thefuel additive in small bottles suitable for direct addition to fuelstorage tanks or vehicle tanks.

By diesel fuel we include any fuel suitable for use in a diesel engineeither for road use or non-road use. This includes but is not limited tofuels described as diesel, marine diesel, heavy fuel oil, industrialfuel oil, etc.

The diesel fuel composition used in the present invention may comprise apetroleum-based fuel oil, especially a middle distillate fuel oil. Suchdistillate fuel oils generally boil within the range of from 110° C. to500° C., e.g. 150° C. to 400° C. The diesel fuel may compriseatmospheric distillate or vacuum distillate, cracked gas oil, or a blendin any proportion of straight run and refinery streams such as thermallyand/or catalytically cracked and hydro-cracked distillates.

The diesel fuel composition may comprise non-renewable Fischer-Tropschfuels such as those described as GTL (gas-to-liquid) fuels, CTL(coal-to-liquid) fuels and OTL (oil sands-to-liquid).

The diesel fuel composition may comprise a renewable fuel such as abiofuel composition or biodiesel composition.

The diesel fuel composition may comprise 1st generation biodiesel. Firstgeneration biodiesel contains esters of, for example, vegetable oils,animal fats and used cooking fats. This form of biodiesel may beobtained by transesterification of oils, for example rapeseed oil,soybean oil, canola oil, safflower oil, palm oil, corn oil, peanut oil,cotton seed oil, tallow, coconut oil, physic nut oil (Jatropha),sunflower seed oil, used cooking oils, hydrogenated vegetable oils orany mixture thereof, with an alcohol, usually a monoalcohol, usually inthe presence of a catalyst.

The diesel fuel composition may comprise second generation biodiesel.Second generation biodiesel is derived from renewable resources such asvegetable oils and animal fats and processed, often in the refinery,using, for example, hydroprocessing such as the H-Bio process developedby Petrobras. Second generation biodiesel may be similar in propertiesand quality to petroleum based fuel oil streams, for example renewablediesel produced from vegetable oils, animal fats etc. and marketed byConocoPhillips as Renewable Diesel and by Neste as NExBTL.

The diesel fuel composition may comprise third generation biodiesel.Third generation biodiesel utilises gasification and Fischer-Tropschtechnology including those described as BTL (biomass-to-liquid) fuels.Third generation biodiesel does not differ widely from some secondgeneration biodiesel, but aims to exploit the whole plant (biomass) andthereby widens the feedstock base.

The diesel fuel composition may contain blends of any or all of theabove diesel fuel compositions.

In some embodiments the diesel fuel composition may be a blended dieselfuel comprising bio-diesel. In such blends the bio-diesel may be presentin an amount of, for example up to 0.5%, up to 1%, up to 2%, up to 3%,up to 4%, up to 5%, up to 10%, up to 20%, up to 30%, up to 40%, up to50%, up to 60%, up to 70%, up to 80%, up to 90%, up to 95% or up to 99%.

In some embodiments the fuel composition may comprise neat biodiesel.

In some preferred embodiments the fuel composition comprises at least 5wt % biodiesel. In some embodiments the fuel composition may comprise aneat GTL fuel.

In some embodiments the diesel fuel composition may comprise a secondaryfuel, for example ethanol. Preferably however the diesel fuelcomposition does not contain ethanol.

The diesel fuel composition used in the present invention may contain arelatively high sulphur content, for example greater than 0.05% byweight, such as 0.1% or 0.2%.

However, in preferred embodiments the diesel fuel composition has asulphur content of at most 0.05% by weight, more preferably of at most0.035% by weight, especially of at most 0.015%. Fuels with even lowerlevels of sulphur are also suitable such as, fuels with less than 50 ppmsulphur by weight, preferably less than 20 ppm, for example 10 ppm orless.

The diesel fuel composition of the present invention preferablycomprises at least 5 wt % biodiesel and less than 50 ppm sulphur.

The quaternary ammonium salt additives of the present invention havebeen found to be effective at controlling deposits in fuel andlubricating compositions.

The present invention may provide the use of a quaternary ammoniumcompound of the first aspect as an additive for fuel or lubricating oilcompositions.

The present invention may provide the use of a quatemary ammoniumcompound of the first aspect as a deposit control additive for fuel orlubricating oil compositions.

The present invention may provide the use of a quatemary ammoniumcompound of the first aspect as a deposit control additive forlubricating oil compositions.

The present invention may provide the use of a quatemary ammoniumcompound of the first aspect as a deposit control additive for fuelcompositions.

The present invention may provide the use of a quatemary ammoniumcompound of the first aspect as a deposit control additive for dieselfuel compositions.

According to a fourth aspect of the present invention there is providedthe use of a quaternary ammonium compound of formula (I):

wherein R⁰, R¹, R² and R³ is each individually an optionally substitutedalkyl, alkenyl or aryl group, X is a linking group, R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is 0 or a positive integer, providedthat n is not 0 when R⁵ is hydrogen as an additive in a fuel orlubricant composition.

Preferred features of the fourth aspect are as defined in relation tothe first, second and third aspects.

The use of the fourth aspect preferably relates to use of the quaternaryammonium salt as a fuel additive, preferably a diesel fuel additive.

Preferably the use of the fourth aspect relates to the use of thequaternary ammonium salt of the first aspect as a detergent additive.

The fourth aspect of the present invention may provide the use of aquaternary ammonium compound of formula (I) to improve the performanceof an engine. The use is suitably achieved when a composition comprisingthe quaternary ammonium compound is combusted in the engine.

Preferably the engine is a diesel engine.

According to a fifth aspect of the present invention there is provided amethod of improving the performance of an engine, the method comprisingcombusting in the engine a fuel composition comprising as an additive aquaternary ammonium compound of formula (I):

wherein R⁰, R¹, R² and R³ is each independently an optionallysubstituted hydrocarbyl group, X is a linking group, R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is 0 or a positive integer, providedthat n is not 0 when R⁵ is hydrogen.

Preferred features of the fifth aspect of the invention are as definedin relation to the first, second, third and fourth aspects.

The method of the fifth aspect preferably involves combusting in theengine a composition of the third aspect.

The fifth aspect of the invention relates to a method of improving theperformance of an engine.

Preferably the engine is a diesel engine.

Most preferably the engine is a direct injection diesel engine.

The present invention relates to improving the performance of dieselengines by combusting diesel fuel compositions comprising a quaternaryammonium salt additive.

Preferably the improvement in performance of the engine is achieved bycombatting deposits in the engine.

In preferred embodiments the fifth aspect of the present inventionrelates to a method of combatting deposits in an engine, preferably adiesel engine.

The method may be achieved by combusting in the engine a compositionquaternary ammonium salt additive which functions as a detergent.

Thus the present invention may provide a method of combatting depositsin a diesel engine, the method comprising combusting in the engine afuel composition comprising as an additive a quaternary ammonium salt ofthe first aspect.

Suitably the use of the fourth aspect of an engine improves theperformance of an engine, preferably a diesel engine. This improvementin performance may, for example, be achieved by combatting deposits inthe engine.

The fourth aspect of the present invention relates to the use of thequaternary ammonium salt additive as a detergent.

References herein to improving performance and/or combating deposits mayapply to either the fourth and/or the fifth aspect of the invention.

The quatemary ammonium salt additives used in the present invention havebeen found to be particularly effective in modern diesel engines havinga high pressure fuel system. Some features of engines of this type havebeen previously described herein.

Suitably the present invention combats deposits and/or improvesperformance of a diesel engine having a high pressure fuel system.Suitably the diesel engine has a pressure in excess of 1350 bar(1.35×10⁸ Pa). It may have a pressure of up to 2000 bar (2×10⁸ Pa) ormore.

Two non-limiting examples of such high pressure fuel systems are: thecommon rail injection system, in which the fuel is compressed utilizinga high-pressure pump that supplies it to the fuel injection valvesthrough a common rail; and the unit injection system which integratesthe high-pressure pump and fuel injection valve in one assembly,achieving the highest possible injection pressures exceeding 2000 bar(2×10⁸ Pa). In both systems, in pressurising the fuel, the fuel getshot, often to temperatures around 100° C., or above.

In common rail systems, the fuel is stored at high pressure in thecentral accumulator rail or separate accumulators prior to beingdelivered to the injectors. Often, some of the heated fuel is returnedto the low pressure side of the fuel system or returned to the fueltank. In unit injection systems the fuel is compressed within theinjector in order to generate the high injection pressures. This in turnincreases the temperature of the fuel.

In both systems, fuel is present in the injector body prior to injectionwhere it is heated further due to heat from the combustion chamber. Thetemperature of the fuel at the tip of the injector can be as high as250-350° C.

Thus the fuel is stressed at pressures from 1350 bar (1.35×10⁸ Pa) toover 2000 bar (2×10⁸ Pa) and temperatures from around 100° C. to 350° C.prior to injection, sometimes being recirculated back within the fuelsystem thus increasing the time for which the fuel experiences theseconditions.

A common problem with diesel engines is fouling of the injector,particularly the injector body, and the injector nozzle. Fouling mayalso occur in the fuel filter. Injector nozzle fouling occurs when thenozzle becomes blocked with deposits from the diesel fuel. Fouling offuel filters may be related to the recirculation of fuel back to thefuel tank. Deposits increase with degradation of the fuel. Deposits maytake the form of carbonaceous coke-like residues, lacquers or sticky orgum-like residues. Diesel fuels become more and more unstable the morethey are heated, particularly if heated under pressure. Thus dieselengines having high pressure fuel systems may cause increased fueldegradation. In recent years the need to reduce emissions has led to thecontinual redesign of injection systems to help meet lower targets. Thishas led to increasingly complex injectors and lower tolerance todeposits.

The problem of injector fouling may occur when using any type of dieselfuels. However, some fuels may be particularly prone to cause fouling orfouling may occur more quickly when these fuels are used. For example,fuels containing biodiesel and those containing metallic species maylead to increased deposits.

When injectors become blocked or partially blocked, the delivery of fuelis less efficient and there is poor mixing of the fuel with the air.Over time this leads to a loss in power of the engine, increased exhaustemissions and poor fuel economy.

Deposits are known to occur in the spray channels of the injector,leading to reduced flow and power loss. As the size of the injectornozzle hole is reduced, the relative impact of deposit build up becomesmore significant. Deposits are also known to occur at the injector tip.Here, they affect the fuel spray pattern and cause less effectivecombustion and associated higher emissions and increased fuelconsumption.

In addition to these “external” injector deposits in the nozzle hole andat the injector tip which lead to reduced flow and power loss, depositsmay occur within the injector body causing further problems. Thesedeposits may be referred to as internal diesel injector deposits (orIDIDs). IDIDs occur inside the injector on the critical moving parts.They can hinder the movement of these parts affecting the timing andquantity of fuel injection. Since modern diesel engines operate undervery precise conditions these deposits can have a significant impact onperformance.

IDIDs cause a number of problems, including power loss and reduced fueleconomy due to less than optimal fuel metering and combustion. Initiallythe user may experience cold start problems and/or rough engine running.These deposits can lead to more serious injector sticking. This occurswhen the deposits stop parts of the injector from moving and thus theinjector stops working. When several or all of the injectors stick theengine may fail completely.

The CEC have recently introduced an Internal Diesel Injector DepositTest, CEC F-110-16, to discriminate between fuels that differ in theirability to produce IDID in direct injection common rail diesel engines.

As mentioned above, the problem of injector fouling may be more likelyto occur when using fuel compositions comprising metal species. Variousmetal species may be present in fuel compositions. This may be due tocontamination of the fuel during manufacture, storage, transport or useor due to contamination of fuel additives. Metal species may also beadded to fuels deliberately. For example, transition metals aresometimes added as fuel borne catalysts, for example to improve theperformance of diesel particulate filters.

Problems of injector sticking may occur when metal or ammonium species,particularly sodium species, react with carboxylic acid species in thefuel.

Sodium contamination of diesel fuel and the resultant formation ofcarboxylate salts is believed to be a major cause of injector sticking.

In some embodiments the diesel fuel compositions used in the presentinvention comprise sodium and/or calcium. Suitably they comprise sodium.The sodium and/or calcium is typically present in a total amount of from0.01 to 50 ppm, preferably from 0.05 to 5 ppm preferably 0.1 to 2 ppmsuch as 0.1 to 1 ppm.

Other metal-containing species may also be present as a contaminant, forexample through the corrosion of metal and metal oxide surfaces byacidic species present in the fuel or from lubricating oil. In use,fuels such as diesel fuels routinely come into contact with metalsurfaces for example, in vehicle fuelling systems, fuel tanks, fueltransportation means etc. Typically, metal-containing contamination maycomprise transition metals such as zinc, iron and copper; Group I orGroup II metals and other metals such as lead.

The presence of metal containing species may give rise to fuel filterdeposits and/or external injector deposits including injector tipdeposits and/or nozzle deposits.

In addition to metal-containing contamination which may be present indiesel fuels there are circumstances where metal-containing species maydeliberately be added to the fuel. For example, as is known in the art,metal-containing fuel-borne catalyst species may be added to aid withthe regeneration of particulate traps. The presence of such catalystsmay also give rise to injector deposits when the fuels are used indiesel engines having high pressure fuel systems.

Metal-containing contamination, depending on its source, may be in theform of insoluble particulates or soluble compounds or complexes.Metal-containing fuel-borne catalysts are often soluble compounds orcomplexes or colloidal species.

In some embodiments, the diesel fuel may comprise metal-containingspecies comprising a fuel-borne catalyst. Preferably, the fuel bornecatalyst comprises one or more metals selected from iron, cerium,platinum, manganese, Group I and Group II metals e.g., calcium andstrontium. Most preferably the fuel borne catalyst comprises a metalselected from iron and cerium.

In some embodiments, the diesel fuel may comprise metal-containingspecies comprising zinc. Zinc may be present in an amount of from 0.01to 50 ppm, preferably from 0.05 to 5 ppm, more preferably 0.1 to 1.5ppm.

Typically, the total amount of all metal-containing species in thediesel fuel, expressed in terms of the total weight of metal in thespecies, is between 0.1 and 50 ppm by weight, for example between 0.1and 20 ppm, preferably between 0.1 and 10 ppm by weight, based on theweight of the diesel fuel.

It is advantageous to provide a diesel fuel composition which preventsor reduces the occurrence of deposits in a diesel engine. In someembodiments such deposits may include “external” injector deposits suchas deposits in and around the nozzle hole and at the injector tip. Insome preferred embodiments the deposits include “internal” injectordeposits or IDIDs. Such fuel compositions may be considered to perform a“keep clean” function i.e. they prevent or inhibit fouling. It is alsobe desirable to provide a diesel fuel composition which would help cleanup deposits of these types. Such a fuel composition which when combustedin a diesel engine removes deposits therefrom thus effecting the“clean-up” of an already fouled engine.

As with “keep clean” properties, “clean-up” of a fouled engine mayprovide significant advantages. For example, superior clean up may leadto an increase in power and/or an increase in fuel economy. In additionremoval of deposits from an engine, in particular from injectors maylead to an increase in interval time before injector maintenance orreplacement is necessary thus reducing maintenance costs.

Although for the reasons mentioned above deposits in injectors is aparticular problem found in modern diesel engines with high pressurefuels systems, it is desirable to provide a diesel fuel compositionwhich also provides effective detergency in older traditional dieselengines such that a single fuel supplied at the pumps can be used inengines of all types.

It is also desirable that fuel compositions reduce the fouling ofvehicle fuel filters. It is useful to provide compositions that preventor inhibit the occurrence of fuel filter deposits i.e. provide a “keepclean” function. It is useful to provide compositions that removeexisting deposits from fuel filter deposits i.e. provide a “clean up”function. Compositions able to provide both of these functions areespecially useful.

The method of the present invention is particularly effective atcombatting deposits in a modern diesel engine having a high pressurefuel system.

Such diesel engines may be characterised in a number of ways.

Such engines are typically equipped with fuel injection equipmentmeeting or exceeding “Euro 5” emissions legislation or equivalentlegislation in the US or other countries.

Such engines are typically equipped with fuel injectors having aplurality of apertures, each aperture having an inlet and an outlet.

Such engines may be characterised by apertures which are tapered suchthat the inlet diameter of the spray-holes is greater than the outletdiameter.

Such modern engines may be characterised by apertures having an outletdiameter of less than 500 μm, preferably less than 200 μm, morepreferably less than 150 μm, preferably less than 100 μm, mostpreferably less than 80 μm or less.

Such modern diesel engines may be characterised by apertures where aninner edge of the inlet is rounded.

Such modern diesel engines may be characterised by the injector havingmore than one aperture, suitably more than 2 apertures, preferably morethan 4 apertures, for example 6 or more apertures.

Such modern diesel engines may be characterised by an operating tiptemperature in excess of 250° C.

Such modern diesel engines may be characterised by a fuel injectionsystem which provides a fuel pressure of more than 1350 bar, preferablymore than 1500 bar, more preferably more than 2000 bar. Preferably, thediesel engine has fuel injection system which comprises a common railinjection system.

The method of the present invention preferably combats deposits in anengine having one or more of the above-described characteristics.

The use of the present invention preferably improves the performance ofan engine. This improvement in performance is suitably achieved byreducing deposits in the engine.

The first aspect of the present invention relates to a method ofcombating deposits in a diesel engine. Combating deposits may involvereducing or the preventing of the formation of deposits in an enginecompared to when running the engine using unadditised fuel. Such amethod may be regarded as achieving “keep clean” performance.

Combating deposits may involve the removal of existing deposits in anengine. This may be regarded as achieving “clean up” performance.

In especially preferred embodiments the method of the fifth aspect andthe use of the fourth aspect of the present invention may be used toprovide “keep clean” and “clean up” performance.

As explained above deposits may occur at different places within adiesel engine, for example a modern diesel engine.

The present invention is particularly useful in the prevention orreduction or removal of internal deposits in injectors of enginesoperating at high pressures and temperatures in which fuel may berecirculated and which comprise a plurality of fine apertures throughwhich the fuel is delivered to the engine. The present invention findsutility in engines for heavy duty vehicles and passenger vehicles.Passenger vehicles incorporating a high speed direct injection (or HSDI)engine may for example benefit from the present invention.

The present invention may also provide improved performance in moderndiesel engines having a high pressure fuel system by controllingexternal injector deposits, for example those occurring in the injectornozzle and/or at the injector tip. The ability to provide control ofinternal injector deposits and external injector deposits is a usefuladvantage of the present invention.

Suitably the present invention may reduce or prevent the formation ofexternal injector deposits. It may therefore provide “keep clean”performance in relation to external injector deposits. Suitably thepresent invention may reduce or remove existing external injectordeposits. It may therefore provide “clean up” performance in relation toexternal injector deposits.

Suitably the present invention may reduce or prevent the formation ofinternal diesel injector deposits. It may therefore provide “keep clean”performance in relation to internal diesel injector deposits.

Suitably the present invention may reduce or remove existing internaldiesel injector deposits. It may therefore provide “clean up”performance in relation to internal diesel injector deposits.

The present invention may also combat deposits on vehicle fuel filters.This may include reducing or preventing the formation of deposits (“keepclean” performance) or the reduction or removal of existing deposits(“clean up” performance).

The removal or reduction of IDIDs according to the present inventionwill lead to an improvement in performance of the engine.

The improvement in performance of the diesel engine system may bemeasured by a number of ways. Suitable methods will depend on the typeof engine and whether “keep clean” and/or “clean up” performance ismeasured.

An improvement in “keep clean” performance may be measured by comparisonwith a base fuel. “Clean up” performance can be observed by animprovement in performance of an already fouled engine.

The effectiveness of fuel additives is often assessed using a controlledengine test.

In Europe the Co-ordinating European Council for the development ofperformance tests for transportation fuels, lubricants and other fluids(the industry body known as CEC), has developed a test for additives formodern diesel engines such as HSDI engines. The CEC F-98-08 test is usedto assess whether diesel fuel is suitable for use in engines meeting newEuropean Union emissions regulations known as the “Euro 5” regulations.The test is based on a Peugeot DW10 engine using Euro 5 injectors, andis commonly referred to as the DW10B test. This test measures power lossin the engine due to deposits on the injectors, and is further describedin example 4.

Preferably the use of the fuel composition of the present inventionleads to reduced deposits in the DW10B test. For “keep clean”performance a reduction in the occurrence of deposits is preferablyobserved.

For “clean up” performance removal of deposits is preferably observed.The DW10B test is used to measure the power loss in modern dieselengines having a high pressure fuel system.

Suitably the use of a fuel composition of the present invention mayprovide a “keep clean” performance in modern diesel engines, that is theformation of deposits in the injectors of these engines may be inhibitedor prevented. Preferably this performance is such that a power loss ofless than 5%, preferably less than 2% is observed after 32 hours asmeasured by the DW10B test.

Suitably the use of a fuel composition of the present invention mayprovide a “clean up” performance in modern diesel engines that is,deposits on the injectors of an already fouled engine may be removed.Preferably this performance is such that the power of a fouled enginemay be returned to within 1% of the level achieved when using cleaninjectors within 16 hours, preferably 12 hours, more preferably 8 hoursas measured in the DW10B test.

In some preferred embodiments, clean up may also provide a powerincrease. Thus a fouled engine may be treated to remove the existingdeposits and provide an additional power gain.

Clean injectors can include new injectors or injectors which have beenremoved and physically cleaned, for example in an ultrasound bath.

The CEC have also developed a new test, commonly known as the DW10Cwhich assesses the ability of a fuel composition to prevent theformation of IDIDs that lead to injector sticking. This test isdescribed in example 5. A modified version of this test adapted tomeasure clean up, is described in example 6.

The DW10C test may be used to measure the “keep clean” or “clean up”performance of an engine.

In some embodiments the present invention provides a “keep clean”performance in relation to the formation of IDIDs. Such performance maybe illustrated by achieving a merit score of at least 7 as measured bythe DW10C test, preferably at least 8, more preferably at least 9.

In some embodiments a merit score of at least 9.3 may be achieved, forexample at least 9.4, at least 9.5, at least 9.6 or at least 9.7.

In some embodiments the present invention provides a “clean-up”performance in relation to IDIDs, whereby existing IDIDs may be removed.Such a performance is illustrated in the examples.

The diesel fuel compositions of the present invention may also provideimproved performance when used with traditional diesel engines.Preferably the improved performance is achieved when using the dieselfuel compositions in modern diesel engines having high pressure fuelsystems and when using the compositions in traditional diesel engines.This is important because it allows a single fuel to be provided thatcan be used in new engines and older vehicles.

For older engines an improvement in performance may be measured usingthe XUD9 test. This test is described in relation to example 5.

Suitably the use of a fuel composition of the present invention mayprovide a “keep clean” performance in traditional diesel engines, thatis the formation of deposits on the injectors of these engines may beinhibited or prevented. Preferably this performance is such that a flowloss of less than 50%, preferably less than 30% is observed after 10hours as measured by the XUD-9 test.

Suitably the use of a fuel composition of the present invention mayprovide a “clean up” performance in traditional diesel engines, that isdeposits on the injectors of an already fouled engine may be removed.Preferably this performance is such that the flow loss of a fouledengine may be reduced by 10% or more within 10 hours as measured in theXUD-9 test.

The benefits provided by the present invention mean that engines need tobe serviced less frequently, leading to cost savings and an increase inmaintenance intervals.

Preferably the method and use of the present invention provide animprovement in the performance of a diesel engine. This improvement inperformance is suitably selected from one or more of:

-   -   a reduction in power loss of the engine;    -   a reduction in external diesel injector deposits;    -   a reduction in internal diesel injector deposits;    -   an improvement in fuel economy;    -   a reduction in fuel filter deposits;    -   a reduction in emissions; and    -   an increase in maintenance intervals.

The additives of the present invention may provide a further benefit inaddition to those listed above. For example the additive may providelubricity benefits and/or corrosion inhibition and/or cold flowimprovement.

The diesel fuel compositions of the present invention may include one ormore further additives such as those which are commonly found in dieselfuels. These include, for example, antioxidants, dispersants,detergents, metal deactivating compounds, wax anti-settling agents, coldflow improvers, cetane improvers, dehazers, stabilisers, demulsifiers,antifoams, corrosion inhibitors, lubricity improvers, dyes, markers,combustion improvers, metal deactivators, odour masks, drag reducers andconductivity improvers. Examples of suitable amounts of each of thesetypes of additives will be known to the person skilled in the art.

In some embodiments the combination of an additive of the invention anda further additive may provide synergistic improvement in performance.

For example the use of a quaternary ammonium salt additive of theinvention in combination with a cold flow improver may provide anunexpected improvement in detergency and/or cold flow performancecompared with the performance of the individual additives used alone.

In some embodiments the use of a quaternary ammonium salt additive ofthe present invention may enable a lower treat rate of cold flowimprover to be used.

For example the use of a quaternary ammonium salt additive of theinvention in combination with a corrosion inhibitor may provide anunexpected improvement in detergency and/or corrosion inhibitioncompared with the performance of the individual additives used alone.

In some embodiments the use of a quaternary ammonium salt additive ofthe present invention may enable a lower treat rate of corrosioninhibitor to be used.

For example the use of a quaternary ammonium salt additive of theinvention in combination with a lubricity improver may provide anunexpected improvement in detergency and/or lubricity compared with theperformance of the individual additives used alone.

In some embodiments the use of a quaternary ammonium salt additive ofthe present invention may enable a lower treat rate of lubricityimprover to be used.

In some preferred embodiments the diesel fuel composition of the presentinvention comprises one or more further detergents. Nitrogen-containingdetergents are preferred.

The one or more further detergents may provide a synergistic benefitsuch that an improved performance is observed when using the combinationof a quaternary ammonium salt additive of the invention and anitrogen-containing detergent compared to the use of an equivalentamount of either additive alone.

The use of a combination of a quaternary ammonium salt additive and anitrogen-containing detergent may also combat deposits and improveperformance in a traditional diesel engine.

The one or more further detergents may be selected from:

-   -   (i) a quaternary ammonium salt additive which is not a compound        of formula (I);    -   (ii) the product of a Mannich reaction between an aldehyde, an        amine and an optionally substituted phenol;    -   (iii) the reaction product of a carboxylic acid-derived        acylating agent and an amine;    -   (iv) the reaction product of a carboxylic acid-derived acylating        agent and hydrazine;    -   (v) a salt formed by the reaction of a carboxylic acid with        di-n-butylamine or tri-n-butylamine;    -   (vi) the reaction product of a hydrocarbyl-substituted        dicarboxylic acid or anhydride and an amine compound or salt        which product comprises at least one amino triazole group; and    -   (vii) a substituted polyaromatic detergent additive.

Preferably one or more further detergents are selected from one or moreof:

-   -   (i) a quaternary ammonium salt additive which is not a compound        of formula (I);    -   (ii) the product of a Mannich reaction between an aldehyde, an        amine and an optionally substituted phenol; and    -   (iii) the reaction product of a carboxylic acid-derived        acylating agent and an amine.

The ratio of the quaternary ammonium salt additive to the nitrogencontaining detergent is suitable from 5:1 to 1:5, preferably from 2:1 to1:2.

In some embodiments the diesel fuel composition further comprises (i) aquaternary ammonium salt additive which is not a compound of formula(I).

The quaternary ammonium salt additive is suitably the reaction productof a nitrogen-containing species having at least one tertiary aminegroup and a quaternising agent.

The nitrogen containing species may be selected from:

-   -   (x) the reaction product of a hydrocarbyl-substituted acylating        agent and a compound comprising at least one tertiary amine        group and a primary amine, secondary amine or alcohol group;    -   (y) a Mannich reaction product comprising a tertiary amine        group; and    -   (z) a polyalkylene substituted amine having at least one        tertiary amine group.

Examples of quaternary ammonium salt and methods for preparing the sameare described in the following patents, which are hereby incorporated byreference, US2008/0307698, US2008/0052985, US2008/0113890 andUS2013/031827.

The preparation of some suitable quaternary ammonium salt additives inwhich the nitrogen-containing species includes component (x) isdescribed in WO 2006/135881 and WO2011/095819.

Component (y) is a Mannich reaction product having a tertiary amine. Thepreparation of quaternary ammonium salts formed from nitrogen-containingspecies including component (y) is described in US 2008/0052985.

The preparation of quaternary ammonium salt additives in which thenitrogen-containing species includes component (z) is described forexample in US 2008/0113890.

To form the quaternary ammonium salt additive (i) thenitrogen-containing species having a tertiary amine group is reactedwith a quaternising agent.

The quaternising agent may suitably be selected from esters andnon-esters.

Preferred quaternising agents for use herein include dimethyl oxalate,methyl 2-nitrobenzoate, methyl salicylate and styrene oxide or propyleneoxide optionally in combination with an additional acid.

An especially preferred additional quaternary ammonium salt for useherein is formed by reacting methyl salicylate or dimethyl oxalate withthe reaction product of a polyisobutylene-substituted succinic anhydridehaving a PIB number average molecular weight of 700 to 1300 anddimethylaminopropylamine.

Other suitable quaternary ammonium salts include quaternisedterpolymers, for example as described in US2011/0258917; quaternisedcopolymers, for example as described in US2011/0315107; and theacid-free quaternised nitrogen compounds disclosed in US2012/0010112.

Further suitable quaternary ammonium compounds for use in the presentinvention include the quaternary ammonium compounds described in theapplicants copending applications WO2011095819, WO2013/017889,WO2015/011506, WO2015/011507, WO2016/016641 and PCT/GB2016/052312.

In some embodiments the diesel fuel composition used in the presentinvention comprises from 1 to 500 ppm, preferably 50 to 250 ppm of thequaternary ammonium salt additive of the present invention and from 1 to500 ppm, preferably 50 to 250 ppm of a further quaternary ammoniumadditive (i).

In some embodiments the diesel fuel composition comprises further (ii)the product of a Mannich reaction between an aldehyde, an amine and anoptionally substituted phenol. This Mannich reaction product is suitablynot a quaternary ammonium salt.

Preferably the aldehyde component used to prepare the Mannich additiveis an aliphatic aldehyde. Preferably the aldehyde has 1 to 10 carbonatoms. Most preferably the aldehyde is formaldehyde.

Suitable amines for use in preparing the Mannich additive includemonoamines and polyamines. One suitable monoamine is butylamine.

The amine used to prepare the Mannich additive is preferably apolyamine. This may be selected from any compound including two or moreamine groups. Preferably the polyamine is a polyalkylene polyamine,preferably a polyethylene polyamine. Most preferably the polyaminecomprises tetraethylenepentamine or ethylenediamine.

The optionally substituted phenol component used to prepare the Mannichadditive may be substituted with 0 to 4 groups on the aromatic ring (inaddition to the phenol OH). For example it may be ahydrocarbyl-substituted cresol. Most preferably the phenol component isa mono-substituted phenol. Preferably it is a hydrocarbyl substitutedphenol. Preferred hydrocarbyl substituents are alkyl substituents having4 to 28 carbon atoms, especially 10 to 14 carbon atoms. Other preferredhydrocarbyl substituents are polyalkenyl substituents. Suchpolyisobutenyl substituents having a number average molecular weight offrom 400 to 2500, for example from 500 to 1500.

In some embodiments the diesel fuel composition of the present inventioncomprises from 1 to 500 ppm, preferably 50 to 250 ppm of a quaternaryammonium salt of the first aspect and from 1 to 500 ppm, preferably 50to 250 ppm of a Mannich additive (ii).

In some embodiments the diesel fuel composition further comprises (iii)the reaction product of a carboxylic acid-derived acylating agent and anamine.

These may also be referred to herein in general as acylatednitrogen-containing compounds.

Suitable acylated nitrogen-containing compounds may be made by reactinga carboxylic acid acylating agent with an amine and are known to thoseskilled in the art.

Preferred hydrocarbyl substituted acylating agents are polyisobutenylsuccinic anhydrides. These compounds are commonly referred to as“PIBSAs” and are known to the person skilled in the art.

Conventional polyisobutenes and so-called “highly-reactive”polyisobutenes are suitable for use in the invention.

Especially preferred PIBSAs are those having a PIB molecular weight (Mn)of from 300 to 2800, preferably from 450 to 2300, more preferably from500 to 1300.

In preferred embodiments the reaction product of the carboxylic acidderived acylating agent and an amine includes at least one primary orsecondary amine group.

A preferred acylated nitrogen-containing compound for use herein isprepared by reacting a poly(isobutene)-substituted succinic acid-derivedacylating agent (e.g., anhydride, acid, ester, etc.) wherein thepoly(isobutene) substituent has a number average molecular weight (Mn)of between 170 to 2800 with a mixture of ethylene polyamines having 2 toabout 9 amino nitrogen atoms, preferably about 2 to about 8 nitrogenatoms, per ethylene polyamine and about 1 to about 8 ethylene groups.These acylated nitrogen compounds are suitably formed by the reaction ofa molar ratio of acylating agent:amino compound of from 10:1 to 1:10,preferably from 5:1 to 1:5, more preferably from 2:1 to 1:2 and mostpreferably from 2:1 to 1:1. In especially preferred embodiments, theacylated nitrogen compounds are formed by the reaction of acylatingagent to amino compound in a molar ratio of from 1.8:1 to 1:1.2,preferably from 1.6:1 to 1:1.2, more preferably from 1.4:1 to 1:1.1 andmost preferably from 1.2:1 to 1:1. Acylated amino compounds of this typeand their preparation are well known to those skilled in the art and aredescribed in for example EP0565285 and U.S. Pat. No. 5,925,151.

In some preferred embodiments the composition comprises a detergent ofthe type formed by the reaction of a polyisobutene-substituted succinicacid-derived acylating agent and a polyethylene polyamine. Suitablecompounds are, for example, described in WO2009/040583.

In some embodiments the diesel fuel composition of the present inventioncomprises from 1 to 500 ppm, preferably 50 to 250 ppm of a quaternaryammonium salt of the first aspec and from 1 to 500 ppm, preferably 50 to250 ppm of an additive which is the reaction product of an acylatingagents and an amine (iii).

In some embodiments the diesel fuel composition comprises (iv) thereaction product of a carboxylic acid-derived acylating agent andhydrazine.

Suitably the additive comprises the reaction product between ahydrocarbyl-substituted succinic acid or anhydride and hydrazine.

Preferably, the hydrocarbyl group of the hydrocarbyl-substitutedsuccinic acid or anhydride comprises a C₈-C₃₆ group, preferably a C₈-C₁₈group. Alternatively, the hydrocarbyl group may be a polyisobutylenegroup with a number average molecular weight of between 200 and 2500,preferably between 800 and 1200.

Hydrazine has the formula NH₂—NH₂. Hydrazine may be hydrated ornon-hydrated. Hydrazine monohydrate is preferred.

The reaction between the hydrocarbyl-substituted succinic acid oranhydride and hydrazine produces a variety of products, such as isdisclosed in US 2008/0060259.

In some embodiments the diesel fuel composition further comprises (v) asalt formed by the reaction of a carboxylic acid with di-n-butylamine ortri-n-butylamine. Exemplary compounds of this type are described in US2008/0060608.

Such additives may suitably be the di-n-butylamine or tri-n-butylaminesalt of a fatty acid of the formula [R′(COOH)_(x)]_(y), where each R′ isa independently a hydrocarbon group of between 2 and carbon atoms, and xis an integer between 1 and 4.

In a preferred embodiment, the carboxylic acid comprises tall oil fattyacid (TOFA).

Further preferred features of additives of this type are described inEP1900795.

In some embodiments the diesel fuel composition further comprises (vi)the reaction product of a hydrocarbyl-substituted dicarboxylic acid oranhydride and an amine compound or salt which product comprises at leastone amino triazole group.

Further preferred features of additive compounds of this type are asdefined in US2009/0282731.

In some embodiments the diesel fuel composition further comprises (vii)a substituted polyaromatic detergent additive.

One preferred compound of this type is the reaction product of anethoxylated naphthol and paraformaldehyde which is then reacted with ahydrocarbyl substituted acylating agent.

Further preferred features of these detergents are described inEP1884556.

Any feature of the invention may be combined with any other feature asappropriate.

The invention will now be further described with reference to thefollowing non-limiting examples. In the examples which follow the valuesgiven in parts per million (ppm) for treat rates denote active agentamount, not the amount of a formulation as added, and containing anactive agent. All parts per million are by weight.

Example 1

Additive A1, a quaternary ammonium salt additive of the invention wasprepared as follows:

(a) A mixture of alkenes having 20 to 24 carbon atoms was heated with1.2 molar equivalents of maleic anhydride. On completion of the reactionexcess maleic anhydride was removed by distillation. The anhydride valueof the substituted succinic anhydride product was measured as 2.591mmolg⁻¹.

This product was then heated with one molar equivalent of polypropyleneglycol having a number average molecular weight of 425, and the reactionwas monitored by FTIR to provide the half ester/half acid product.

(b) 1 molar equivalent of diethyl ethanolamine was reacted with 1.5molar equivalents of butylene oxide and 6 molar equivalents of water at60° C. in toluene for 10 hours in the presence of the half ester/halfacid provided in the step (a) to form a quaternary ammonium compound.Volatiles were removed in vacuo.

Compounds A2 to A21 detailed in table 1 were prepared by an analogousmethod.

TABLE 1 Compound R H—(OR⁴)n-OR⁵ Amine Epoxide A1 C20-24 polypropyleneDiethyl ethanolamine Butylene oxide glycol Mn425 A2 C20-24 polypropyleneDimethyl ethanolamine Butylene oxide glycol Mn425 A3 C20-24polypropylene Triethylamine Butylene oxide glycol Mn425 A4 C20-24polypropylene Tributylamine Butylene oxide glycol Mn425 A5 C20-24tripropylene glycol Dimethyl ethanolamine Butylene oxide A6 C20-24tripropylene glycol Diethyl ethanolamine Butylene oxide A7 C20-24tripropylene glycol Triethylamine Butylene oxide A8 C20-24 tripropyleneglycol Tributylamine Butylene oxide A9 C20-24 triethyleneglycol Dimethylethanolamine Butylene oxide A10 C20-24 triethyleneglycol Diethylethanolamine Butylene oxide A11 C20-24 triethyleneglycol TriethylamineButylene oxide A12 C20-24 triethyleneglycol Tributylamine Butylene oxideA13 C20-24 polypropylene Dimethyl ethanolamine Butylene oxide glycolMn725 A14 C20-24 polypropylene Diethyl ethanolamine Butylene oxideglycol Mn725 A15 C20-24 polypropylene Triethylamine Butylene oxideglycol Mn725 A16 C20-24 polypropylene Tributylamine Butylene oxideglycol Mn725 A17 C20-24 Tetraethyleneglycol Dimethyl ethanolamineButylene oxide A18 C20-24 Tetraethyleneglycol Diethyl ethanolamineButylene oxide A19 C20-24 tetraethyleneglycol Triethylamine Butyleneoxide A20 C20-24 tetraethyleneglycol Tributylamine Butylene oxide A21C20-24 polyethyleneglycol Dimethyl ethanolamine Butylene oxide Mn400 A22C20-24 2-Ethylhexanol N,N-diethyl ethanolamine Butylene oxide A23 C20-24Butanol N,N-diethyl ethanolamine Butylene oxide A24 C20-24 Poly(ethylene2-[2-(Dimethylamino)ethoxy] 1,2- glycol) Mn400 ethanol epoxydodecane A25C20-24 Poly(ethylene N,N-dimethyl Benzylamine 2-Ethylhexyl glycol) Mn400Glycidyl Ether A26 C20-24 Poly(ethylene N,N-dimethyl ethanolamine 1,2-glycol) Mn400 epoxydodecane A27 C20-24 Poly(ethylene N,N-dimethylethanolamine Styrene Oxide glycol) Mn400 A28 C20-24 Poly(ethyleneN,N-Dimethyl 2-Ethylhexyl glycol) Mn400 octadecylamine Glycidyl EtherA29 C20-24 Poly(ethylene N,N-Dimethyl Butylene oxide glycol) Mn400octadecylamine A30 C20-24 Poly(ethylene N,N-Dimethyl 1,2- glycol) Mn400octadecylamine epoxydodecane A31 C20-24 Poly(ethylene N,N-DimethylStyrene Oxide glycol) Mn400 octadecylamine A32 C20-24 Poly(propyleneN,N-dimethyl Benzylamine 2-Ethylhexyl glycol) Mn425 Glycidyl Ether A33C20-24 Poly(propylene N,N-dimethyl Benzylamine Butylene oxide glycol)Mn425 A34 C20-24 Poly(propylene N,N-dimethyl Benzylamine Styrene Oxideglycol) Mn425 A35 C20-24 Poly(propylene N,N-dimethyl ethanolamine 1,2-glycol) Mn425 epoxydodecane A36 C20-24 Poly(propylene N,N-Dimethyl2-Ethylhexyl glycol) Mn425 octadecylamine Glycidyl Ether A37 C20-24Poly(propylene N,N-Dimethyl Butylene oxide glycol) Mn425 octadecylamineA38 C20-24 Poly(propylene N,N-Dimethyl Styrene Oxide glycol) Mn425octadecylamine A39 C20-24 Tetradecanol N,N-diethyl ethanolamine Butyleneoxide A40 C20-24 Tri(propylene 2-[2-(Dimethylamino)ethoxy] 2-Ethylhexylglycol) ethanol Glycidyl Ether A41 C20-24 Tri(propylene2-[2-(Dimethylamino)ethoxy] 1,2- glycol) ethanol epoxydodecane A42C20-24 Tri(propylene 2-[2-(Dimethylamino)ethoxy] Styrene Oxide glycol)ethanol A43 C20-24 Tri(propylene N,N-dimethyl Benzylamine 2-Ethylhexylglycol) Glycidyl Ether A44 C20-24 Tri(propylene N,N-dimethyl BenzylamineButylene oxide glycol) A45 C20-24 Tri(propylene N,N-dimethyl Benzylamine1,2- glycol) epoxydodecane A46 C20-24 Tri(propylene N,N-dimethylBenzylamine Styrene Oxide glycol) A47 C20-24 Tri(propylene N,N-dimethylethanolamine 1,2- glycol) epoxydodecane A48 C20-24 Tri(propyleneN,N-Dimethyl 2-Ethylhexyl glycol) octadecylamine Glycidyl Ether A49C20-24 Tri(propylene N,N-Dimethyl Butylene oxide glycol) octadecylamineA50 C20-24 Tri(propylene N,N-Dimethyl 1,2- glycol) octadecylamineepoxydodecane A51 C20-24 Tri(propylene N,N-Dimethyl Styrene Oxideglycol) octadecylamine A52 1000PIB Tri(propylene N,N-dimethylethanolamine 1,2- glycol) epoxydodecane

Example 2

Diesel fuel compositions were prepared by dosing additives to aliquotsall drawn from a common batch of RF06 base fuel.

The compositions were tested in a screening test which correlates withperformance at combatting IDIDs as measured in the DW10C test.

In this test a fuel composition is tested using a Jet Fuel ThermalOxidation Test equipment. In this modified test 800 ml of fuel is flowedover a heated tube at pressures of approximately 540 psi. The testduration is 2.5 hours. At the end of the test the amount of depositobtained on the tube is compared to a reference value.

The value shown in table 2 is the percentage reduction in depositthickness compared to base fuel.

TABLE 2 ppm Average thickness Compound active (% reduction) A1(inventive) 120 95 A3 (inventive) 120 97 A4 (inventive) 120 95 A6(inventive) 120 84 A7 (inventive) 120 98 A8 (inventive) 120 97 A10(inventive) 120 92 A11 (inventive) 120 92 A12 (inventive) 120 91 A14(inventive) 120 99 A15 (inventive) 120 91 A16 (inventive) 120 98 A19(inventive) 120 91 A20 (inventive) 120 91 A22 (inventive) 120 81 A23(inventive) 120 91 A24 (inventive) 120 98 A25 (inventive) 120 80 A26(inventive) 120 98 A27 (inventive) 120 81 A28 (inventive) 120 79 A29(inventive) 120 90 A30 (inventive) 120 97 A31 (inventive) 120 100 A32(inventive) 120 95 A33 (inventive) 120 92 A34 (inventive) 120 90 A35(inventive) 120 94 A36 (inventive) 120 91 A37 (inventive) 120 99 A38(inventive) 120 96 A40 (inventive) 120 85 A41 (inventive) 120 82 A42(inventive) 120 85 A43 (inventive) 120 90 A44 (inventive) 120 97 A45(inventive) 120 99 A46 (inventive) 120 78 A47 (inventive) 120 97 A48(inventive) 120 87 A49 (inventive) 120 91 A50 (inventive) 120 99 A51(inventive) 120 78 C1 (comparative) 120 0 C2 (comparative) 120 2

Comparative additive C₁ is dodecenyl substituted succinic acid.

Comparative additive C₂ is a polyisobutenyl (PIB) substituted succinicacid where the PIB has a number average molecular weight of 1000.

Table 3 below shows the specification for RF06 base fuel.

TABLE 3 Limits Property Units Min Max Method Cetane Number 52.0 54.0 ENISO 5165 Density at 15° C. kg/m³ 833 837 EN ISO 3675 Distillation 50%v/v Point ° C. 245 — 95% v/v Point ° C. 345 350 FBP ° C. — 370 FlashPoint ° C. 55 — EN 22719 Cold Filter Plugging ° C. — −5 EN 116 PointViscosity at 40° C. mm²/sec 2.3 3.3 EN ISO 3104 Polycyclic Aromatic %m/m 3.0 6.0 IP 391 Hydrocarbons Sulphur Content mg/kg — 10 ASTM D 5453Copper Corrosion — 1 EN ISO 2160 Conradson Carbon % m/m — 0.2 EN ISO10370 Residue on 10% Dist. Residue Ash Content % m/m — 0.01 EN ISO 6245Water Content % m/m — 0.02 EN ISO 12937 Neutralisation (Strong mg KOH/g— 0.02 ASTM D 974 Acid) Number Oxidation Stability mg/mL — 0.025 EN ISO12205 HFRR (WSD1, 4) μm — 400 CEC F-06-A-96 Fatty Acid Methyl prohibitedEster

Example 3

The performance of fuel compositions of example 2 in modern dieselengines having a high pressure fuel system may be tested according tothe CECF-98-08 DW 10 method. This is referred to herein as the DW10Btest.

The engine of the injector fouling test is the PSA DW10BTED4. Insummary, the engine characteristics are:

Design: Four cylinders in line, overhead camshaft, turbocharged with EGR

Capacity: 1998 cm³

Combustion chamber: Four valves, bowl in piston, wall guided directinjection

Power: 100 kW at 4000 rpm

Torque: 320 Nm at 2000 rpm

Injection system: Common rail with piezo electronically controlled6-hole injectors.

Max. pressure: 1600 bar (1.6×10⁸ Pa). Proprietary design by SIEMENS VDO

Emissions control: Conforms with Euro IV limit values when combined withexhaust gas post-treatment system (DPF)

This engine was chosen as a design representative of the modern Europeanhigh-speed direct injection diesel engine capable of conforming topresent and future European emissions requirements. The common railinjection system uses a highly efficient nozzle design with roundedinlet edges and conical spray holes for optimal hydraulic flow. Thistype of nozzle, when combined with high fuel pressure has allowedadvances to be achieved in combustion efficiency, reduced noise andreduced fuel consumption, but are sensitive to influences that candisturb the fuel flow, such as deposit formation in the spray holes. Thepresence of these deposits causes a significant loss of engine power andincreased raw emissions.

The test is run with a future injector design representative ofanticipated Euro V injector technology.

It is considered necessary to establish a reliable baseline of injectorcondition before beginning fouling tests, so a sixteen hour running-inschedule for the test injectors is specified, using non-foulingreference fuel.

Full details of the CEC F-98-08 test method can be obtained from theCEC. The coking cycle is summarised below.

1. A warm up cycle (12 minutes) according to the following regime:

Duration Engine Speed Torque Step (minutes) (rpm) (Nm) 1 2 idle <5 2 32000 50 3 4 3500 75 4 3 4000 100

2. 8 hrs of engine operation consisting of 8 repeats of the followingcycle

Duration Engine Speed Load Torque Boost Air After IC Step (minutes)(rpm) (%) (Nm) (° C.) 1 2 1750 (20) 62 45 2 7 3000 (60) 173  50 3 2 1750(20) 62 45 4 7 3500 (80) 212  50 5 2 1750 (20) 62 45 6 10 4000 100  * 507 2 1250 (10) 20 43 8 7 3000 100  * 50 9 2 1250 (10) 20 43 10 10 2000100  * 50 11 2 1250 (10) 20 43 12 7 4000 100  * 50 * for expected rangesee CEC method CEC-F-98-08

3. Cool down to idle in 60 seconds and idle for 10 seconds

4. 4 hrs soak period

The standard CEC F-98-08 test method consists of 32 hours engineoperation corresponding to 4 repeats of steps 1-3 above, and 3 repeatsof step 4. ie 56 hours total test time excluding warm ups and cooldowns.

Example 4

The ability of additives of the invention to remove ‘Internal DieselInjector Deposits’ (IDIDs) may be measured according to the test methodCEC F-110-16, available from the Co-ordinating European Council. Thetest uses the PSA DW10C engine.

The engine characteristics as follows:

Design: Four cylinders in line, overhead camshaft, variable geometryturbocharger with EGR Capacity: 1997 cm³ Combustion Four valves, bowl inpiston, direct injection chamber: Power: 120 kW @ 3750 rpm Torque: 340Nm @ 2000 rpm Injection Common rail with solenoid type injectors system:Delphi Injection System Emissions Conforms to Euro V limit values whencombined with control: exhaust gas post-treatment system.

The test fuel (RF06) is dosed with 0.5 mg/kg Na in the form of SodiumNaphthenate+10 mg/kg Dodecyl Succinic Acid (DDSA).

The test procedure consists of main run cycles followed by soak periods,before cold starts are carried out.

The main running cycle consist of two speed and load set points,repeated for 6 hrs, as seen below and in FIG. 1.

Speed Torque Duration Step (rpm) (N · m) (s) 1 3750 280  1470 1 - Ramp →2 — — 30 2 1000 10 270 2 - Ramp → 1 — — 30

The ramp times of 30 seconds included in the duration of each step.

During the main run, parameters including, Throttle pedal position, ECUfault codes, Injector balance coefficient and Engine stalls are observedand recorded.

The engine is then left to soak at ambient temperature for 8 hrs.

After the soak period the engine is re-started. The starter is operatedfor 5 seconds; if the engine fails to start the engine is left for 60seconds before a further attempt. A maximum of 5 attempts are allowed.

If the engine starts the engine is allowed to idle for 5 minutes.Individual exhaust temperatures are monitored and the maximumTemperature Delta is recorded. An increased variation inCylinder-to-Cylinder exhaust temperatures is a good indication thatinjectors are suffering from IDID. Causing them to either open slowly orstay open to long.

An example in FIG. 2 of all exhaust temperatures with <30° C. deviation,indicating no sticking caused by IDID.

The complete test comprises of 6× Cold Starts, although the Zero hourCold Start does not form part of the Merit Rating and 5×6 hr Main runcycles, giving a total of 30 hrs engine running time. The recorded datais inputted into the Merit Rating Chart. This allows a Rating to beproduced for the test. Maximum rating of 10 shows no issues with therunning or operability of the engine for the duration of the test.

An example below:

Cold start Starting Exhaust temperature consistency Number Exhaust ofTemperature Attempts Max Cyl. Cold Start Maximum (1 = Maximum DeviationStart Y/N Merits first start) Deduction Merits Merits (° C.) DeductionMerits #0 not rated #1 Y 5 1 0 5 5 21.8 0 5 #2 Y 5 1 0 5 5 18.1 0 5 #3 Y5 1 0 5 5 15.5 0 5 #4 Y 5 1 0 5 5 20.2 0 5 #5 Y 5 1 0 5 5 22.6 0 5 Total25 25 merits Main run Operabiity Max Pedal Max Number Position Inject.of ECU at 1000 Balancing Main Maximum Fault Deduc- Stall Deduct- rpm/10Deduc- Coeff. Deduc- run Merits resets tion (Y/N) ion N.m (%) tion (rpm)tion Merits #1 5 0 0 N 0 15.4 0 15 0 5 #2 5 0 0 N 0 13.5 0 15 0 5 #3 5 00 N 0 13.6 0 16 0 5 #4 5 0 0 N 0 13.8 0 15 0 5 #5 5 0 0 N 0 14.5 0 15 05 25 Global Rating-Summary (Merit/10) 10

Example 5

The effectiveness of the additives of the invention in older traditionaldiesel engine types was assessed using a standard industry test—CEC testmethod No. CEC F-23-A-01.

This test measures injector nozzle coking using a Peugeot XUD9 A/LEngine and provides a means of discriminating between fuels of differentinjector nozzle coking propensity. Nozzle coking is the result of carbondeposits forming between the injector needle and the needle seat.Deposition of the carbon deposit is due to exposure of the injectorneedle and seat to combustion gases, potentially causing undesirablevariations in engine performance.

The Peugeot XUD9 A/L engine is a 4 cylinder indirect injection Dieselengine of 1.9 litre swept volume, obtained from Peugeot Citroen Motorsspecifically for the CEC PF023 method.

The test engine is fitted with cleaned injectors utilising unflattedinjector needles. The airflow at various needle lift positions have beenmeasured on a flow rig prior to test. The engine is operated for aperiod of 10 hours under cyclic conditions.

Time Speed Torque Stage (secs) (rpm) (Nm) 1 30 1200 ± 30 10 ± 2 2 603000 ± 30 50 ± 2 3 60 1300 ± 30 35 ± 2 4 120 1850 ± 30 50 ± 2

The propensity of the fuel to promote deposit formation on the fuelinjectors is determined by measuring the injector nozzle airflow againat the end of test, and comparing these values to those before test. Theresults are expressed in terms of percentage airflow reduction atvarious needle lift positions for all nozzles. The average value of theairflow reduction at 0.1 mm needle lift of all four nozzles is deemedthe level of injector coking for a given fuel.

The results of this test using the specified additive combinations ofthe invention are shown in table 3. In each case the specified amount ofactive additive was added to an RF06 base fuel meeting the specificationgiven in table 2 (example 5) above.

The invention claimed is:
 1. A composition comprising a diesel fuel anda quaternary ammonium compound of formula (I):

wherein R⁰, R¹, R² and R³ is each independently an optionallysubstituted hydrocarbyl group, X is a linking group, R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is a positive integer.
 2. A methodof improving the performance of an engine, the method comprisingcombusting in the engine a diesel fuel composition comprising as anadditive a quaternary ammonium compound of formula (I):

wherein R⁰, R¹, R² and R³ is each independently an optionallysubstituted hydrocarbyl group, X is a linking group, R⁴ is an optionallysubstituted alkylene group, R⁵ is hydrogen or an optionally substitutedalkyl, alkenyl or aryl group, and n is a positive integer.
 3. Thecomposition according to claim 1 wherein —OCXCOO—(R⁴O)_(n)—R⁵ is derivedfrom a hydrocarbyl substituted succinic acid or a hydrocarbylsubstituted succinic anhydride.
 4. The composition according to claim 1wherein each R⁴ is ethylene or propylene.
 5. The composition accordingto claim 1 wherein R⁵ is hydrogen and n is at least
 1. 6. Thecomposition according to claim 1 wherein R⁵ is an optionally substitutedalkyl group having 4 to 40 carbon atoms and n is from 1 to
 40. 7. Thecomposition according to claim 1 wherein each of R¹ and R² isindependently an optionally substituted alkyl group having from 1 to 12carbon atoms.
 8. The composition according to claim 1 wherein R³ is analkyl or hydroxyalkyl group having 1 to 10 carbon atoms.
 9. Thecomposition according to claim 1 wherein R³ is selected from the groupconsisting of: (1) a polyisobutenyl group having a molecular weight offrom 100 to 5000; (2) an optionally substituted alkylene phenol moietyof formula (A) or (B)

wherein n in structure (A) or (B) is 0 to 4, R^(x) is an optionallysubstituted hydrocarbyl group, R^(y) is an optionally substituted alkyl,alkenyl or aryl group; and L is a linking group; and (3) a succinimidemoiety of formula:

wherein R^(z) is an optionally substituted hydrocarbyl group and L is alinking group.
 10. The composition according to claim 1 wherein R⁰ as isa group of formula:

wherein each of R⁹, R¹⁰, R¹¹, R¹² is independently selected fromhydrogen or an optionally substituted alkyl, alkenyl or aryl group. 11.The composition according to claim 1 wherein X is an optionallysubstituted alkylene or arylene group.
 12. The composition according toclaim 1 wherein the quaternary ammonium compound is the reaction productof: (a) a tertiary amine of formula R¹R²R³N wherein each of, R¹, R² andR³ is independently an optionally substituted alkyl group having 1 to 12carbon atoms; (b) an epoxide selected from styrene oxide, ethyleneoxide, propylene oxide, butylene oxide, epoxyhexane, octene oxide,stilbene oxide, 2-ethylhexyl glycidyl ether, 1,2-epoxydodecane and otheralkyl and alkenyl epoxides having 2 to 50 carbon atoms; and (c) acompound of formula HOOCXCOO—(R⁴O)_(n)—R⁵ wherein X is CH₂CHR or CHRCH₂wherein R is an optionally substituted hydrocarbyl group; and n is morethan 1, R⁴ is an ethylene or propylene group and R⁵ is hydrogen; or n is1 and R⁵ is a C1 to C20 alkyl group.
 13. The composition according toclaim 1 wherein the quaternary ammonium compound is the reaction productof: (a) a tertiary amine of formula R¹R²R³N wherein each of, R¹, R² andR³ is independently an alkyl or hydroxyalkyl group having 1 to 6 carbonatoms; (b) an epoxide selected from propylene oxide, butylene oxide and2-ethylhexyl glycidyl ether; and (c) a compound of formulaHOOCXCOO—(R⁴O)_(n)—R⁵ which is the reaction product of a succinic acidor anhydride having a C₂₀ to C₂₄ alkyl or alkenyl substituent and analcohol selected from polypropylene glycol having a number averagemolecular weight of 300 to 800, 2-ethylhexanol and butanol.
 14. Thecomposition according to claim 1 further comprising one or moredetergents selected from the group consisting of: (i) a furtherquaternary ammonium salt additive; (ii) the product of a Mannichreaction between an aldehyde, an amine and an optionally substitutedphenol; (iii) the reaction product of a carboxylic acid-derivedacylating agent and an amine; (iv) the reaction product of a carboxylicacid-derived acylating agent and hydrazine; (v) a salt formed by thereaction of a carboxylic acid with di-n-butylamine or tri-n-butylamine;(vi) the reaction product of a hydrocarbyl-substituted dicarboxylic acidor anhydride and an amine compound or salt which product comprises atleast one amino triazole group; and (vii) a substituted polyaromaticdetergent additive.
 15. The composition according to claim 1 wherein thecomposition comprises a mixture of two or more quarternary ammonium saltadditives.
 16. The method as defined in claim 2 wherein the additive isused as a detergent to combat deposits in a diesel fuel composition in adiesel engine.
 17. The method according to claim 2 which is carried outin a diesel engine having a pressure in excess of 1350 bar.
 18. Themethod according to claim 2 which achieves “keep clean” performance. 19.The method according to claim 2 which achieves “clean up” performance.20. The method according to claim 16 wherein the deposits are injectordeposits.
 21. The method according to claim 20 wherein the deposits areinternal diesel injector deposits.
 22. The method according to claim 2which achieves an improvement in performance of one or more of: areduction in power loss of the engine; a reduction in external dieselinjector deposits; a reduction in internal diesel injector deposits; animprovement in fuel economy; a reduction in fuel filter deposits; areduction in emissions; or an increase in maintenance intervals.
 23. Themethod according to claim 22 which provides an improvement inperformance in diesel engines having a pressure in excess of 1350 barand provides an improvement in performance in traditional dieselengines.
 24. The composition according to claim 1 which furthercomprises one or more further additives selected from the groupconsisting of: lubricity improvers, corrosion inhibitors and cold flowimprovers.